Supplemental Prospectus (Form 424B5)

Filed Pursuant to Rule 424(b)(5)

Registration No. 333-278041

PROSPECTUS SUPPLEMENT

(To Prospectus dated March 18, 2024)

 

2,884,615 Shares of Class A Common Stock

We are offering to certain institutional and accredited investors (the "Investors") 2,884,615 shares of Class A common stock, $0.0001 par value per share (the "Class A Common Stock"), of the Company, at the offering price of $52.00 per share, in a registered direct offering pursuant this prospectus supplement and the accompanying prospectus and a securities purchase agreement dated May 12, 2026, by between the Company and the Investors (the "Purchase Agreement").

Our Class A Common Stock is listed on the Nasdaq Global Market under the symbol "ACMR." The last reported sale price of our Class A Common Stock on the Nasdaq Global Market on May 11, 2026 was $64.67 per share.

Investing in our Class A Common Stock involves a high degree of risk. You should carefully read and consider this prospectus supplement, the accompanying prospectus, the documents incorporated by reference herein and therein, and the risk factors described in, and incorporated by reference under, "Risk Factors" beginning on page S-4 of this prospectus supplement, and under similar headings in the other documents in the other documents incorporated by reference herein before investing in any securities.

Neither the Securities and Exchange Commission nor any state securities commission has approved or disapproved of these securities or determined if this prospectus is truthful or complete. Any representation to the contrary is a criminal offense.

Delivery of the Class A Common Stock is expected to be made on or about May 15, 2026, subject to customary closing conditions.

The date of this prospectus is May 12, 2026

TABLE OF CONTENTS

Prospectus Supplement

Prospectus

ABOUT THIS PROSPECTUS SUPPLEMENT

This prospectus supplement and the accompanying prospectus are part of a registration statement that we have filed with the United States Securities and Exchange Commission, or SEC, utilizing a "shelf" registration process.

We provide information to you about this offering of shares of our Class A Common Stock in two separate documents that are bound together: (1) this prospectus supplement, which describes the specific terms and details regarding this offering and also adds to and updates information contained in the accompanying prospectus and the documents incorporated by reference therein; and (2) the accompanying base prospectus, which provides general information, some of which may not apply to this offering. Generally, when we refer to this "prospectus," we are referring to both documents combined. If information in this prospectus supplement is inconsistent with the accompanying base prospectus, you should rely on this prospectus supplement. However, if any statement in one of these documents is inconsistent with a statement in a document having a later date incorporated by reference in this prospectus supplement, the statement in the document incorporated by reference modifies or supersedes the earlier statement as our business, financial condition, results of operations and prospects may have changed since the earlier dates.

You should rely only on the information contained in, or incorporated by reference into, this prospectus supplement, the accompanying prospectus or in any other prospectus supplement or free writing prospectus that we may authorize for use in connection with this offering. We have not authorized any other person to provide you with different or additional information. If anyone provides you with different, additional or inconsistent information, you should not rely on it. We are not making an offer to sell or soliciting an offer to buy our securities in any jurisdiction in which an offer or solicitation is not authorized or in which the person making that offer or solicitation is not qualified to do so or to anyone to whom it is unlawful to make an offer or solicitation. You should assume that the information appearing in this prospectus supplement, the base prospectus, the documents incorporated by reference into this prospectus supplement and the base prospectus, and in any free writing prospectus that we may authorize for use in connection with this offering, is accurate only as of the date of those respective documents. Our business, financial condition, results of operations and prospects may have changed since those dates. You should read this prospectus supplement, the accompanying prospectus, the documents incorporated by reference herein and therein, and any free writing prospectus that we may authorize for use in connection with this offering, in their entirety before making an investment decision. You should also read and consider the information in the documents to which we have referred you in the sections of this prospectus entitled "Where You Can Find More Information" and "Incorporation of Certain Documents by Reference."

We are offering to sell, and seeking offers to buy, shares of Class A Common Stock only in jurisdictions where offers and sales are permitted. The distribution of this prospectus and the offering of the Class A Common Stock in certain jurisdictions may be restricted by law. Persons outside the United States who come into possession of this prospectus supplement and the accompanying prospectus must inform themselves about, and observe any restrictions relating to, the offering of the Class A Common Stock and the distribution of this prospectus outside the United States. This prospectus supplement and the accompanying prospectus does not constitute, and may not be used in connection with, an offer to sell, or a solicitation of an offer to buy, any securities offered by this prospectus by any person in any jurisdiction in which it is unlawful for such person to make such an offer or solicitation.

When we refer to "ACMR," "we," "our," "us" or the "Company" in this prospectus supplement, we mean ACM Research, Inc., and our consolidated subsidiaries unless otherwise specified. When we refer to "you," we mean prospective investors in the Company.

Our logo design is one of our trademarks. This prospectus also includes trademarks, tradenames, and service marks that are the property of other organizations. For convenience, our logo appears in this prospectus without the ™ symbol, but those uses are not intended to indicate that we will not assert, to the fullest extent under applicable law, our rights to this trademark.

PROSPECTUS SUPPLEMENT SUMMARY

This summary description about us and our business highlights selected information contained elsewhere in this prospectus supplement or incorporated in this prospectus supplement by reference. This summary does not contain all of the information you should consider before buying our securities. You should carefully read this entire prospectus supplement, the accompanying prospectus, and any free writing prospectus, including each of the documents incorporated herein or therein by reference, before making an investment decision.

Overview

We supply advanced, innovative capital equipment developed for the global semiconductor industry.

Our products are designed to address yield-critical and performance-sensitive process steps that become increasingly difficult as semiconductor devices scale to smaller geometries and more complex structures. We focus on developing differentiated process solutions that enable effective particle removal, uniform material deposition, and reliable process control, while helping customers manage cost of ownership, throughput, and environmental considerations. We believe this approach has supported broader adoption of our tools across multiple technology nodes and device types.

Fabricators of advanced integrated circuits, or chips, can use our wet-cleaning, plating, furnace, PECVD, track, and other front-end processing equipment in numerous steps to improve product yield, even at increasingly advanced process nodes. We have designed these products for use in fabricating foundry, logic and memory chips, including dynamic random-access memory, or DRAM, and 3D NAND-flash memory chips. We also develop, manufacture and sell a range of advanced packaging equipment to wafer assembly and packaging customers.

We incorporated in California in January 1998 and redomesticated in Delaware in November 2016. Our headquarters are located at 42307 Osgood Road, Suite I, Fremont, California 94539, where our telephone number is (510) 445-3700. Our website address is www.acmr.com. The information contained on our website is not incorporated by reference into this prospectus supplement, and you should not consider any information contained on, or that can be accessed through, our website as part of this prospectus supplement, or in deciding whether to purchase our securities.

THE OFFERING

Class A Common Stock offered by us

2,884,615 shares of our Class A Common Stock.

Class A Common Stock to be outstanding immediately after the offering

64,117,679 shares of our Class A Common Stock, which is based on 61,233,064 shares of Class A Common Stock outstanding as of May 5, 2026, and excludes:

Use of proceeds

We estimate that the net proceeds to us from this offering will be approximately $150 million, after deducting estimated offering expenses payable by us. We intend to use the net proceeds from this offering for the purpose of funding our U.S. and global expansion, as well as general corporate expenses.

Risk factors

Investing in our Class A Common Stock involves significant risks. Please read the information contained in and incorporated by reference under the heading "Risk Factors" on page S-4 of this prospectus supplement and under similar headings in the other documents that are filed after the date hereof and incorporated by reference into this prospectus supplement, together with the other information included in or incorporated by reference into this prospectus supplement, before deciding whether to invest in our Class A Common Stock.

Nasdaq Global Market symbol

"ACMR"

RISK FACTORS

Investing in our Class A Common Stock involves a high degree of risk. Before making an investment decision, you should carefully consider the risks and uncertainties described below and discussed under the heading "Risk Factors" contained in our most recent Annual Report on Form 10-K, and in our subsequent Quarterly reports on Form 10-Q, as well as any amendments or updates thereto reflected in our subsequent filings with the Securities and Exchange Commission, or SEC, which are incorporated by reference into this prospectus supplement in their entirety, together with all of the other information in this prospectus supplement and the accompanying prospectus supplement, including our financial statements and related notes incorporated by reference herein and therein, the documents incorporated by reference herein and therein and any free writing prospectus that we may authorize for use in connection with this offering. If any of these risks are realized, our business, financial condition, results of operations and prospects could be materially and adversely affected. In that event, the trading price of our Class A Common Stock could decline and you could lose part or all of your investment. Additional risks and uncertainties that are not yet identified or that we think are immaterial may also materially harm our business, operating results and financial condition and could result in a complete loss of your investment.

Risks related to this offering

We will have broad discretion in how we use the net proceeds of this offering. We may not use these proceeds effectively, which could affect our results of operations and cause our stock price to decline.

Although we currently intend to use the net proceeds from this offering in the manner described in the section entitled "Use of Proceeds" in this prospectus supplement, we will have considerable discretion in the application of the net proceeds of this offering. We may use the net proceeds for purposes that do not yield a significant return or any return at all for our stockholders. In addition, pending their use, we may invest the net proceeds from this offering in a manner that does not produce income or that loses value. If we do not invest or apply the net proceeds from this offering in ways that enhance stockholder value, we may fail to achieve expected financial results, which could cause our stock price to decline.

If we raise additional capital through the sale of shares of our Class A Common Stock, convertible securities or debt in the future, your ownership in us could be diluted and restrictions could be imposed on our business.

In addition to this offering, we may issue shares of our Class A Common Stock or securities convertible into our Class A Common Stock to raise additional capital in the future. To the extent we issue such securities, our stockholders may experience substantial dilution and the trading price of our Class A Common Stock could decline. If we obtain funds through a credit facility or through the issuance of debt or preferred securities, such debt or preferred securities could have rights senior to your rights as a common shareholder, which could impair the value of our Class A Common Stock.

We have not paid dividends in the past and do not expect to pay dividends in the future, and, as a result, any return on investment may be limited to the value of our stock.

We have never declared or paid cash dividends on our capital stock. We intend to retain any future earnings to finance the operation and expansion of our business, and we do not expect to declare or pay any dividends in the foreseeable future. Accordingly, you may only receive a return on your investment in Class A Common Stock if the market price of Class A Common Stock increases.

Our ability to pay dividends on Class A Common Stock depends significantly on our receiving distributions of funds from our subsidiaries in mainland China. Mainland China statutory laws and regulations permit payments of dividends by those subsidiaries only out of their retained earnings, which are determined in accordance with mainland China accounting standards and regulations that differ from U.S. generally accepted accounting principles. Mainland China regulations and our subsidiaries' articles of association require annual appropriations of 10% of net after-tax profits to be set aside, prior to payment of dividends, as a reserve or surplus fund, which restricts our subsidiaries' ability to transfer a portion of their net assets to us. In addition, our subsidiaries' short-term bank loans restrict their ability to pay dividends to us.

The market price of our Class A Common Stock has been and may continue to be volatile, which could result in substantial losses for investors purchasing our shares.

The market price of Class A Common Stock has been, and could continue to be, subject to significant fluctuations. The market price of Class A Common Stock may fluctuate significantly in response to numerous factors, many of which are beyond our control, including:

In recent years, the stock market in general has experienced extreme price and volume fluctuations that have often been unrelated or disproportionate to changes in the operating performance of the companies whose stock is experiencing those price and volume fluctuations. Further, following periods of volatility in the overall market and the market price of a particular company's securities, securities class action litigation has often been instituted against these companies. Similar litigation may be instituted against us in the future, which could result in substantial costs and a diversion of our management's attention and resources.

Sales of a substantial number of shares of our Class A Common Stock in the public market could cause our stock price to fall.

Sales of a substantial number of shares of our Class A Common Stock in the public market or the perception that these sales might occur could depress the market price of our Class A Common Stock and could impair our ability to raise capital through the sale of additional equity securities. We are unable to predict the effect that sales may have on the prevailing market price of our Class A Common Stock. In addition, the sale of substantial amounts of our Class A Common Stock could adversely impact our trading price. The sale or the availability for sale of a large number of shares of our Class A Common Stock in the public market could cause the price of our Class A Common Stock to decline.

If securities or industry analysts do not publish research or reports about us, our business or our market, or if they publish negative evaluations of Class A Common Stock or the stock of other companies in our industry, the price of our stock and trading volume could decline.

The trading market for Class A Common Stock will depend in part on the research and reports that securities or industry analysts publish about us or our business. If one or more of the analysts who cover us downgrade the Class A Common Stock or publish inaccurate or unfavorable research about our business, the Class A Common Stock price would likely decline. In addition, if one or more of these analysts ceases coverage of the Class A Common Stock or fails to publish reports about the Class A Common Stock on a regular basis, we could lose visibility in the financial markets, which in turn could cause the Class A Common Stock price or trading volume to decline.

CAUTIONARY NOTE REGARDING FORWARD-LOOKING STATEMENTS

This prospectus supplement, the accompanying prospectus and the information incorporated by reference herein and therein contain forward-looking statements within the meaning of the Private Securities Litigation Reform Act of 1995. All statements, other than statements of historical facts, included in this prospectus supplement, the accompanying prospectus and the information incorporated by reference herein and therein regarding our strategy, future operations, future financial position, future revenue, projected costs, prospects, plans and objectives of management are forward-looking statements. In some cases, you can identify forward-looking statements by terms such as "may," "might," "will," "objective," "intend," "should," "could," "can," "would," "expect," "believe," "anticipate," "project," "target," "design," "estimate," "predict," "potential," "plan" or the negative of these terms, and similar expressions intended to identify forward-looking statements. These statements reflect our management's current views with respect to future events and are based on their beliefs and assumptions and on information currently available to them. Although we believe that the expectations reflected in these forward-looking statements are reasonable, these statements relate to future events or our future operational or financial performance, and involve known and unknown risks, uncertainties and other factors, including those described or incorporated by reference in "Item 1A. Risk Factors" of Part I of our Annual Report on Form 10-K, filed on March 2, 2026, and "Item 1A. Risk Factors" of Part II of our quarterly report on Form 10-Q for the fiscal quarter, filed on May 8, 2026, that may cause our actual results, performance or achievements to be materially different from any future results, performance or achievements expressed or implied by these forward-looking statements. Forward-looking statements include, but are not limited to, statements that relate to:

The information included under the heading "Item 7. Management's Discussion and Analysis of Financial Condition and Results of Operations-Overview," of Part II of our Annual Report on Form 10-K, filed on March 2, 2026, contains statistical data and estimates, including forecasts, that are based on information provided by Gartner, Inc., or Gartner, in "Forecast: Semiconductor Capital Spending, Wafer Fab Equipment and Capacity, Worldwide, 4Q25 Update" (December 2025), or the Gartner Report. The Gartner Report represents research opinions or viewpoints that are published, as part of a syndicated subscription service, by Gartner and are not representations of fact. The Gartner Report speaks as of its original publication date (and not as of the date of this prospectus supplement, the accompanying prospectus and the information incorporated by reference herein and therein), and the opinions expressed in the Gartner Report are subject to change without notice. While we are not aware of any misstatements regarding any of the data presented from the Gartner Report, estimates, and in particular forecasts, involve numerous assumptions and are subject to risks and uncertainties, as well as change based on various factors, that could cause results to differ materially from those expressed in the data presented in this prospectus supplement, the accompanying prospectus and the information incorporated by reference herein and therein.

Any forward-looking statement made by us in this prospectus supplement, the accompanying prospectus and the information incorporated by reference herein and therein speaks only as of the date on which it is made. Except as required by law, we assume no obligation to update these statements publicly or to update the reasons actual results could differ materially from those anticipated in these statements, even if new information becomes available in the future.

You should read this prospectus supplement, the accompanying prospectus and the information incorporated by reference herein and therein, completely and with the understanding that our actual future results may be materially different from what we expect. We qualify all of our forward-looking statements by these cautionary statements.

USE OF PROCEEDS

We estimate that the net proceeds to us from this offering, after deducting estimated offering expenses payable by us, will be approximately $150 million.

We intend to use the net proceeds from this offering for the purpose of funding our U.S. and global expansion, as well as general corporate expenses.

As of the date of this prospectus supplement, we cannot specify all of the particular uses for the net proceeds to be received upon the completion of this offering. Accordingly, our management and board of directors will have broad discretion in the application and specific allocations of the net proceeds, and investors will be relying on the judgment of our management and board of directors regarding the application of the proceeds of this offering.

These expected uses represent our current intentions based upon our present plans and market conditions. The amounts we actually expend in these areas, and the timing thereof, may vary significantly from our current intentions and will depend upon a number of factors, including research and product development efforts, cash generated from future operations and actual expenses to operate our business.

Pending our use of the net proceeds from this offering, we intend to invest the net proceeds in bank deposits, money market funds, and U.S. government securities.

DIVIDEND POLICY

We have never declared or paid cash dividends on our capital stock. We intend to retain any future earnings to finance the operation and expansion of our business, and we do not expect to declare or pay any dividends in the foreseeable future. Any determination to pay dividends in the future will be at the discretion of our board of directors and will depend on our financial condition, operating results, capital requirements and general business conditions and other factors that our board of directors may deem relevant.

PLAN OF DISTRIBUTION

We have entered into the Purchase Agreement, directly with the Investors in connection with this offering and we will only sell shares of Class A Common Stock to the Investors in this offering who have entered into the Purchase Agreement. Pursuant to the Purchase Agreement, the Investors agreed to purchase, severally and not jointly, 2,884,615 shares of our Class A Common Stock at a purchase price of $52.00 per share. We have agreed to indemnify the Investors against certain liabilities under the Securities Act.

The shares of Class A Common Stock were offered directly to the Investors without a placement agent, underwriter, broker or dealer. All of the Class A Common Stock sold in this offering will be sold at the same price in a single closing. It is possible that not all of the shares we are offering pursuant to this prospectus supplement will be sold at the closing, in which case our net proceeds would be reduced.

We expect to deliver the Class A Common Stock offered pursuant to this prospectus supplement on or about May 15, 2026, subject to the satisfaction of customary closing conditions.

We have agreed to reimburse a fee of $1.25 million (the "Financial Advisor Fees") to financial advisors (the "Financial Advisors") who provided services to us in connection with this offering. We estimate the total expenses of this offering, which will be payable by us, excluding the Financial Advisor Fees, will be approximately $150,000.

We have agreed to a 6-month "lock-up" with respect to the Class A Common Stock and other of our securities. This means that, subject to certain exceptions, for a period of 6 months following the date of this prospectus supplement, we may not offer, sell, pledge or otherwise dispose of these securities without the prior written consent of the Investors' investment advisor.

The public offering price of the securities we are offering was negotiated between us and the Investors, in consultation with the financial advisors based on the trading of our Class A Common Stock prior to the offering, among other things. Other factors considered in determining the public offering price of the securities we are offering include the history and prospects of the Company, the stage of development of our business, our business plans for the future and the extent to which they have been implemented, an assessment of our management, general conditions of the securities markets at the time of the offering and such other factors as were deemed relevant.

The Transfer Agent and Registrar for our ordinary shares is Computershare Trust Company, N.A.

Our Class A Common Stock is traded on The Nasdaq Global Market under the symbol "ACMR".

LEGAL MATTERS

The validity of the shares of Class A Common Stock offered hereby will be passed upon for us by K&L Gates, LLP, Irvine, California.

EXPERTS

The consolidated financial statements of ACM Research, Inc. at December 31, 2025, 2024 and 2023 and for each year then ended, appearing in ACM Research, Inc.'s Annual Reports on Form 10-K for the years ended December 31, 2025, 2024 and 2023 and the effectiveness of ACM Research, Inc.'s internal control over financial reporting as of December 31, 2025, 2024 and 2023 have been audited by Ernst & Young Hua Ming LLP, independent registered public accounting firm, as set forth in their reports thereon, included therein, and incorporated herein by reference. Such consolidated financial statements are incorporated herein by reference in reliance upon such reports given on the authority of such firm as experts in accounting and auditing.

WHERE YOU CAN FIND MORE INFORMATION

We file reports, proxy statements and other information with the SEC. The SEC maintains a website at www.sec.gov that contains reports, proxy and information statements and other information about issuers, such as us, who file electronically with the SEC.

Our website address is www.acmr.com. The information on our website, however, is not, and should not be deemed to be, a part of this prospectus supplement or the accompanying prospectus. We have included our website address as an inactive textual reference only. Through our website, we make available, free of charge, annual, quarterly and current reports, proxy statements, along with amendments thereto, and other information as soon as reasonably practicable after they are electronically filed with, or furnished to, the SEC.

This prospectus supplement and the accompanying prospectus are part of a registration statement on Form S-3 that we filed with the SEC under the Securities Act and do not contain all of the information set forth or incorporated by reference in the registration statement and the exhibits to the registration statement. The full registration statement may be obtained from the SEC or us, as provided below. Forms of the documents establishing the terms of the offered securities are or may be filed as exhibits to the registration statement or documents incorporated by reference in the registration statement. Statements in this prospectus supplement or the accompanying prospectus about these documents are summaries and each statement is qualified in all respects by reference to the document to which it refers. You should refer to the actual documents for a more complete description of the relevant matters. You may inspect a copy of the registration statement through the SEC's website, as provided above. We have not incorporated by reference into this prospectus supplement or the accompanying prospectus the information on our website, and you should not consider it to be a part of this prospectus supplement or the accompanying prospectus.

INCORPORATION OF CERTAIN INFORMATION BY REFERENCE

We have filed a registration statement on Form S-3 with the SEC under the Securities Act. The accompanying prospectus is part of the registration statement but the registration statement includes and incorporates by reference additional information and exhibits. The SEC permits us to "incorporate by reference" the information contained in documents we file with the SEC, which means that we can disclose important information to you by referring you to those documents rather than by including them in this prospectus supplement or the accompanying prospectus. Information that is incorporated by reference is considered to be part of this prospectus supplement and the accompanying prospectus and you should read it with the same care that you read this prospectus supplement and the accompanying prospectus. Later information that we file with the SEC will automatically update and supersede the information that is either contained, or incorporated by reference, in this prospectus supplement and the accompanying prospectus, and will be considered to be a part of this prospectus supplement and the accompanying prospectus from the date those documents are filed. We have filed with the SEC, and incorporate by reference in this prospectus supplement and the accompanying prospectus:

Notwithstanding the statements in the preceding paragraphs, no document, report or exhibit (or portion of any of the foregoing) or any other information that we have "furnished" to the SEC pursuant to the Exchange Act shall be incorporated by reference into this prospectus supplement.

We also incorporate by reference any future filings (other than current reports furnished under Item 2.02 or Item 7.01 of Form 8-K and exhibits filed on such form that are related to such items unless such Form 8-K expressly provides to the contrary) made with the SEC pursuant to Sections 13(a), 13(c), 14 or 15(d) of the Exchange Act until we file a post-effective amendment that indicates the termination of the offering of the securities made by this prospectus supplement and will become a part of this prospectus supplement from the date that such documents are filed with the SEC. Information in such future filings updates and supplements the information provided in this prospectus supplement. Any statements in any such future filings will automatically be deemed to modify and supersede any information in any document we previously filed with the SEC that is incorporated or deemed to be incorporated herein by reference to the extent that statements in the later filed document modify or replace such earlier statements.

You may request a free copy of any of the documents incorporated by reference in this prospectus by writing or telephoning us at the following address:

ACM Research, Inc.

42307 Osgood Road

Suite I

Fremont, California 94539

(510) 445-3700

Attention: Investor Relations

Exhibits to the filings will not be sent, unless those exhibits have been specifically incorporated by reference in this prospectus supplement.

PROSPECTUS

 

Class A Common Stock

Preferred Stock

Debt Securities

Warrants

Units

 

Class A Common Stock

Offered by the Selling Stockholders

We may offer and sell the securities identified above, and the selling stockholders may offer and sell shares of our Class A common stock, in each case, from time to time in one or more offerings. This prospectus provides you with a general description of the securities. We will not receive any proceeds from the sale of our Class A common stock by the selling stockholders.

Each time we or any of the selling stockholders, offer and sell securities, we or any of the selling stockholders will provide a supplement to this prospectus that contains specific information about the offering and the amounts, prices and terms of the securities. The supplement may also add, update or change information contained in this prospectus with respect to that offering. You should carefully read this prospectus and the applicable prospectus supplement before you invest in any of our securities.

We or any of the selling stockholders may offer and sell the securities described in this prospectus and any prospectus supplement to or through one or more underwriters, dealers and agents, or directly to purchasers, or through a combination of these methods. In addition, the selling stockholders may offer and sell shares of our Class A common stock from time to time, together or separately. If any underwriters, dealers or agents are involved in the sale of any of the securities, their names and any applicable purchase price, fee, commission or discount arrangement between or among them will be set forth, or will be calculable from the information set forth, in the applicable prospectus supplement. For more information, please see "About This Prospectus" and "Plan of Distribution" in this prospectus. No securities may be sold without delivery of this prospectus and the applicable prospectus supplement describing the method and terms of the offering of the securities.

Our Class A common stock is listed on the Nasdaq Global Market, or Nasdaq, under the symbol "ACMR". On March 15, 2024, the last reported sale price of our Class A common stock on Nasdaq was $27.11 per share.

Investing in these securities involves significant risks. See "Risk Factors" on page 2 of this prospectus and in any accompanying prospectus supplement, and in the documents incorporated by reference in this prospectus for a discussion of the factors you should carefully consider before deciding to purchase these securities.

Neither the Securities and Exchange Commission nor any state securities commission has approved or disapproved of these securities or passed upon the adequacy or accuracy of this prospectus. Any representation to the contrary is a criminal offense.

The date of this prospectus is March 18, 2024.

TABLE OF CONTENTS

You should rely only on the information contained in or incorporated by reference into this prospectus, in any accompanying prospectus supplement or any free writing prospectuses prepared by or on behalf of us or to which we have referred you. Neither we, nor the selling stockholders have authorized any person to give any information or to make any representations other than those contained or incorporated by reference in this prospectus, any accompanying prospectus supplement, or any free writing prospectuses prepared by or on behalf of us or to which we have referred you, and, if given or made, you must not rely upon the information or representations as having been authorized. This prospectus, any accompanying prospectus supplement and any free writing prospectuses prepared by or on behalf of us or to which we have referred you, do not constitute an offer to sell or the solicitation of an offer to buy securities, nor do this prospectus or any accompanying supplement to this prospectus constitute an offer to sell or the solicitation of an offer to buy securities in any jurisdiction to any person to whom it is unlawful to make such offer or solicitation. The information contained in this prospectus, any accompanying prospectus supplement, and any free writing prospectuses prepared by or on behalf of us or to which we have referred you, speaks only as of the date set forth on the cover page and may not reflect subsequent changes in our business, financial condition, results of operations and prospects even though this prospectus, any accompanying prospectus supplement, and any free writing prospectuses prepared by or on behalf of us or to which we have referred you, is delivered or securities are sold on a later date.

ABOUT THIS PROSPECTUS

This prospectus is part of a registration statement on Form S-3 that we filed with the Securities and Exchange Commission, or the SEC, as a "well-known seasoned issuer" as defined in Rule 405 under the Securities Act of 1933, as amended, or the Securities Act, utilizing a "shelf" registration process. Under this shelf registration statement, we and the selling stockholders to be named in a supplement to this prospectus may sell securities from time to time in one or more offerings, as described in this prospectus. Each time that we or the selling stockholders offer and sell securities, we or the selling stockholders will provide a prospectus supplement to this prospectus that contains specific information about the securities being offered and sold and the specific terms of that offering. We may also authorize one or more free writing prospectuses to be provided to you that may contain material information relating to these offerings. The prospectus supplement or free writing prospectus may also add, update or change information contained in this prospectus with respect to that offering. If there is any inconsistency between the information in this prospectus and the applicable prospectus supplement or free writing prospectus, you should rely on the prospectus supplement or free writing prospectus, as applicable. Before purchasing any securities, you should carefully read both this prospectus and the applicable prospectus supplement (and any applicable free writing prospectuses), together with the additional information described under the heading "Where You Can Find More Information."

We, and the selling stockholders, have not authorized anyone to provide you with any information or to make any representations other than those contained in this prospectus, any applicable prospectus supplement or any free writing prospectuses prepared by or on behalf of us or to which we have referred you. We and the selling stockholders take no responsibility for, and can provide no assurance as to the reliability of, any other information that others may give you. We and the selling stockholders will not make an offer to sell these securities in any jurisdiction where the offer or sale is not permitted. You should assume that the information appearing in this prospectus, any applicable prospectus supplement or any free writing prospectus is accurate only as of the date on its respective cover, that the information appearing in any applicable free writing prospectus is accurate only as of the date of that free writing prospectus, and that any information incorporated by reference is accurate only as of the date of the document incorporated by reference, unless we indicate otherwise. Our business, financial condition, results of operations and prospects may have changed since those dates. This prospectus incorporates by reference, and any prospectus supplement or free writing prospectus may contain and incorporate by reference, market data and industry statistics, estimates and projections that are based on independent industry publications and other publicly available information. Although we believe these sources are reliable, we do not guarantee the accuracy or completeness of this information and we have not independently verified this information. In addition, the market and industry data and forecasts that may be included or incorporated by reference in this prospectus, any prospectus supplement or any applicable free writing prospectus may involve estimates, assumptions and other risks and uncertainties and are subject to change based on various factors, including those discussed under the heading "Risk Factors" contained in this prospectus, the applicable prospectus supplement and any applicable free writing prospectus, and under similar headings in other documents that are incorporated by reference into this prospectus. Accordingly, investors should not place undue reliance on this information.

References in this prospectus to "our company," "our," "us," "we" and similar terms refer to ACM Research, Inc. and not, unless the context otherwise requires, subsidiaries of ACM Research, Inc.

Our logo design is one of our trademarks. This prospectus also includes trademarks, tradenames, and service marks that are the property of other organizations. For convenience, our logo appears in this prospectus without the ™ symbol, but those uses are not intended to indicate that we will not assert, to the fullest extent under applicable law, our rights to this trademark.

ABOUT OUR COMPANY

We supply advanced, innovative capital equipment developed for the global semiconductor industry. Fabricators of advanced integrated circuits, or chips, can use our wet-cleaning and other front-end processing tools in numerous steps to improve product yield, even at increasingly advanced process nodes. We have designed these tools for use in fabricating foundry, logic and memory chips, including dynamic random-access memory and 3D NAND-flash memory chips. We also develop, manufacture and sell a range of advanced packaging tools to wafer assembly and packaging customers.

We incorporated in California in January 1998 and redomesticated in Delaware in November 2016. Our headquarters are located at 42307 Osgood Road, Suite I, Fremont, California 94539, where our telephone number is (510) 445-3700.

RISK FACTORS

Investment in any securities offered pursuant to this prospectus and the applicable prospectus supplement involves risks. Before acquiring any of such securities, you should carefully consider the risk factors incorporated by reference to our most recent Annual Report on Form 10-K and any subsequent Quarterly Reports on Form 10-Q or Current Reports on Form 8-K filed by us, and all other information contained or incorporated by reference into this prospectus, as updated by our filings under the Securities Exchange Act of 1934, as amended, or the Exchange Act, and the risk factors and other information contained in the applicable prospectus supplement and any applicable free writing prospectus. The occurrence of any of these risks might cause you to lose all or part of your investment in the offered securities. This prospectus and the documents incorporated herein by reference also contain forward-looking statements that involve risks and uncertainties. Actual results could differ materially from those anticipated in these forward-looking statements as a result of certain factors, including the risks described in the documents incorporated herein by reference.

FORWARD-LOOKING STATEMENTS AND STATISTICAL DATA

This prospectus and the documents incorporated by reference herein contain forward-looking statements within the meaning of the Private Securities Litigation Reform Act of 1995. All statements, other than statements of historical facts, included or incorporated by reference in this prospectus regarding our strategy, future operations, future financial position, future revenue, projected costs, prospects, plans and objectives of management are forward-looking statements. In some cases, you can identify forward-looking statements by terms such as "may," "might," "will," "objective," "intend," "should," "could," "can," "would," "expect," "believe," "anticipate," "project," "target," "design," "estimate," "predict," "potential," "plan" or the negative of these terms, and similar expressions intended to identify forward-looking statements. These statements reflect our current views with respect to future events and are based on our management's belief and assumptions and on information currently available to our management. Although we believe that the expectations reflected in these forward-looking statements are reasonable, these statements relate to future events or our future operational or financial performance, and involve known and unknown risks, uncertainties and other factors, including those described or incorporated by reference in our most our Annual Report on Form 10-K and any subsequent Quarterly Reports on Form 10-Q or Current Reports on Form 8-K, that may cause our actual results, performance or achievements to be materially different from any future results, performance or achievements expressed or implied by these forward-looking statements.

The information included under the heading "Item 7. Management's Discussion and Analysis of Financial Condition and Results of Operations-Overview," of Part II of our most recent Annual Report on Form 10-K contains statistical data and estimates, including forecasts, that are based on information provided by Gartner, Inc., or Gartner, in "Forecast: Semiconductor Wafer Fab Equipment, Worldwide, 4Q23 Update" (December 2023), or the Gartner Report. The Gartner Report represents research opinions or viewpoints that are published, as part of a syndicated subscription service, by Gartner and are not representations of fact. The Gartner Report speaks as of its original publication date (and not as of the date of this prospectus), and the opinions expressed in the Gartner Report are subject to change without notice. While we are not aware of any misstatements regarding any of the data presented from the Gartner Report, estimates, and in particular forecasts, involve numerous assumptions and are subject to risks and uncertainties, as well as change based on various factors, that could cause results to differ materially from those expressed in the data presented below.

Any forward-looking statement made or incorporated by reference into this prospectus speaks only as of the date on which it is made. Except as required by law, we assume no obligation to update these statements publicly or to update the reasons actual results could differ materially from those anticipated in these statements, even if new information becomes available in the future.

You should read this prospectus and the documents incorporated by reference herein completely and with the understanding that our actual future results may be materially different from what we expect. We qualify all of our forward-looking statements by these cautionary statements.

USE OF PROCEEDS

We intend to use the net proceeds from the sale of securities as set forth in the applicable prospectus supplement. We will not receive any of the proceeds from the sale of Class A common stock being offered by any selling stockholders.

DESCRIPTION OF CAPITAL STOCK

General

As of February 23, 2024, our authorized capital stock consisted of 150,000,000 shares of Class A common stock, $0.0001 par value per share, 5,307,816 shares of Class B common stock, $0.0001 par value per share, and 10,000,000 shares of preferred stock, $0.0001 par value per share. Class A common stock and Class B common stock are referred to collectively as common stock.

The following summary describes our capital stock, including material provisions of our charter, our bylaws and Delaware law. Because the following is only a summary, it does not contain all of the information that may be important to you. For a complete description, you should refer to our charter and bylaws, copies of which are incorporated by reference as exhibits to the registration statement of which this prospectus is a part.

Common Stock

Outstanding Shares and Options

As of February 23, 2024, there were:

Authorized but unissued shares of Class B common stock are not available for reissuance. The actual number of stockholders is greater than the number of record holders and includes stockholders who are beneficial owners but whose shares are held in street name by brokers and other nominees. This number of holders of record also does not include stockholders whose shares may be held in trust by other entities.

Voting Rights

Except as otherwise required by Delaware law, at every annual or special meeting of stockholders, holders of Class B common stock are entitled to 20 votes per share and holders of Class A common stock are entitled to one vote per share. The holders of Class A common stock and Class B common stock vote together as a single class, unless otherwise required by law. Delaware law could require either holders of Class A common stock or Class B common stock to vote separately as a single class in the following circumstances:

Stockholders do not have the ability to cumulate votes for the election of directors. The board of directors is not currently classified. Our charter and bylaws, however, provide for a classified board of directors consisting of three classes of approximately equal size, each serving staggered three-year terms, when the outstanding shares of Class B common stock represent less than a majority of the combined voting power of the common stock. Our directors will be assigned by the then-current board to a class when the outstanding shares of Class B common stock represent less than a majority of the combined voting power of the common stock.

Dividends

Subject to preferences that may be applicable to any then outstanding preferred stock, the holders of our outstanding shares of common stock are entitled to receive dividends, if any, as may be declared from time to time by the board of directors out of legally available funds. The holders of Class A common stock and Class B common stock are entitled to share equally, identically and ratably, on a per share basis, with respect to any dividend or distribution unless different treatment of the shares of each such class is approved by the affirmative vote of the holders of a majority of the outstanding shares of Class A common stock and Class B common stock, each voting separately as a class. At present, we have no plans to issue dividends.

Liquidation

In the event of our liquidation, dissolution or winding up, holders of common stock will be entitled to share ratably in the net assets legally available for distribution to stockholders after the payment of all of our debts and other liabilities, subject to the satisfaction of any liquidation preference granted to the holders of any outstanding shares of preferred stock.

Conversion

Each outstanding share of Class B common stock is convertible into one share of Class A common stock (a) at any time, at the option of the holder, or (b) upon any transfer of such share of Class B common stock, whether or not for value, except for certain transfers described in our charter, including transfers to family members, trusts solely for the benefit of the stockholder or their family members, and partnerships, corporations, and other entities exclusively owned by the stockholder or their family members. In addition, on or after the date of this prospectus, all outstanding shares of Class B common stock will convert automatically into shares of Class A common stock, on a one for one basis, upon the election of the holders of a majority of the then outstanding shares of Class B common stock. Once converted or transferred and converted into Class A common stock, shares of Class B common stock will not be reissued.

Other Rights and Preferences

Other than as described above, holders of common stock have no preemptive, conversion or subscription rights, and there are no redemption or sinking fund provisions applicable to common stock. The rights, preferences and privileges of the holders of common stock are subject to, and may be adversely affected by, the rights of the holders of shares of any series of preferred stock that we may designate and issue in the future.

Preferred Stock

Under the terms of our charter, the board of directors is authorized to issue up to 10,000,000 shares of preferred stock in one or more series, to establish the number of shares to be included in each such series, and to fix the designation, powers, preferences and rights of such shares and any qualifications, limitations or restrictions thereof. These rights, preferences and privileges could include dividend rights, conversion rights, voting rights, terms of redemption, liquidation preferences, sinking fund terms and other provisions, any or all of which may be greater than the rights of common stock. The issuance of preferred stock with voting and conversion rights may adversely affect the voting power of the holders of common stock, including the loss of voting control to others, and the likelihood that such holders will receive dividend payments and payments upon our liquidation. In addition, the issuance of preferred stock could have the effect of delaying, deferring or preventing a change in control of our company or other corporate action.

Anti-Takeover Provision

So long as the outstanding shares of Class B common stock represent a majority of the combined voting power of common stock, the holders of Class B common stock will effectively control all matters submitted to our stockholders for a vote, as well as the overall management and direction of our company, which will have the effect of delaying, deferring or discouraging another person from acquiring control of our company.

After such time as the shares of Class B common stock no longer represent a majority of the combined voting power of common stock, the provisions of Delaware law, and our charter and our bylaws may have the effect of delaying, deferring or discouraging another person from acquiring control of our company.

Delaware Law

Section 203 of the Delaware General Corporation Law prevents some Delaware corporations from engaging, under some circumstances, in a business combination, which includes a merger or sale of at least 10% of the corporation's assets with any interested stockholder, meaning a stockholder who, together with affiliates and associates, owns or, within three years prior to the determination of interested stockholder status, did own 15% or more of the corporation's outstanding voting stock, unless:

A Delaware corporation may "opt out" of these provisions with an express provision in its original charter or an express provision in its charter or bylaws resulting from a stockholders' amendment approved by at least a majority of the outstanding voting shares. We have not opted out of these provisions. As a result, mergers or other takeover or change in control attempts of us may be discouraged or prevented.

Charter and Bylaw Provisions

Our charter and bylaws include a number of provisions that may have the effect of deterring hostile takeovers or delaying or preventing changes in control of our company, even after such time as the shares of Class B common stock no longer represent a majority of the combined voting power of common stock, including the following:

Choice of Forum

Our charter provides that the Court of Chancery of the State of Delaware will be the exclusive forum for: any derivative action or proceeding brought on our behalf; any action asserting a breach of fiduciary duty; any action asserting a claim against us arising pursuant to the Delaware General Corporation Law, or our charter or bylaws; any action to interpret, apply, enforce, or determine the validity of our charter or bylaws; or any action asserting a claim against us that is governed by the internal affairs doctrine. The enforceability of similar choice of forum provisions in other companies' certificates of incorporation has been challenged in legal proceedings, and it is possible that a court could find these types of provisions to be inapplicable or unenforceable.

Transfer Agent and Registrar

The transfer agent and registrar for our common stock is Computershare Trust Company, N.A.

Nasdaq Global Market

The Class A common stock is listed on the Nasdaq Global Market under the symbol "ACMR."

DESCRIPTION OF DEBT SECURITIES

We may issue debt securities from time to time, in one or more series, as either senior or subordinated debt or as senior or subordinated convertible debt. While the terms we have summarized below will apply generally to any debt securities that we may offer under this prospectus, we will describe the particular terms of any debt securities that we may offer in more detail in any applicable prospectus supplement or free writing prospectus. The terms of any debt securities offered under any applicable prospectus supplement may differ from the terms described below. Unless the context requires otherwise, whenever we refer to the indenture, we also are referring to any supplemental indentures that specify the terms of a particular series of debt securities.

We will issue the debt securities under the indenture that we will enter into with the trustee named in the indenture. The indenture will be qualified under the Trust Indenture Act of 1939, as amended, or the Trust Indenture Act. We have filed the form of indenture as an exhibit to the registration statement of which this prospectus is a part, and supplemental indentures and forms of debt securities containing the terms of the debt securities being offered will be filed as exhibits to the registration statement of which this prospectus is a part or will be incorporated by reference from reports that we file with the SEC.

The following summary of material provisions of the debt securities and the indenture is subject to, and qualified in its entirety by reference to, all of the provisions of the indenture applicable to a particular series of debt securities. We urge you to read any applicable prospectus supplements and any related free writing prospectuses related to the debt securities that we may offer under this prospectus, as well as the complete indenture that contains the terms of the debt securities.

General

The indenture does not limit the amount of debt securities that we may issue. It provides that we may issue debt securities up to the principal amount that we may authorize and may be in any currency or currency unit that we may designate. Except for the limitations on consolidation, merger and sale of all or substantially all of our assets contained in the indenture, the terms of the indenture do not contain any covenants or other provisions designed to give holders of any debt securities protection against changes in our operations, financial condition or transactions involving us.

We may issue the debt securities issued under the indenture as "discount securities," which means they may be sold at a discount below their stated principal amount. These debt securities, as well as other debt securities that are not issued at a discount, may be issued with "original issue discount," or OID, for U.S. federal income tax purposes because of interest payment and other characteristics or terms of the debt securities. One or more series of debt securities may be variable rate debt securities that may be exchanged for fixed rate debt securities. Material U.S. federal income tax considerations applicable to debt securities issued with OID will be described in more detail in any applicable prospectus supplement.

We will comply with Section 14(e) under the Exchange Act to the extent applicable, and any other tender offer rules under the Exchange Act, which may then be applicable, in connection with any obligation we may have to purchase debt securities at the option of the holders thereof. Any such obligation applicable to a series of debt securities will be described in any applicable prospectus supplement.

Any applicable prospectus supplement relating to a series of debt securities being offered will contain the following terms, if applicable:

Conversion or Exchange Rights

We will set forth in any applicable prospectus supplement the terms on which a series of debt securities may be convertible into or exchangeable for our common stock or our other securities. We will include provisions as to settlement upon conversion or exchange and whether conversion or exchange is mandatory, at the option of the holder or at our option. We may include provisions pursuant to which the number of shares of our common stock or our other securities that the holders of the series of debt securities receive would be subject to adjustment.

Consolidation, Merger or Sale

Except as set forth in any applicable prospectus supplement, the indenture will provide that we shall not consolidate with, or sell, assign, transfer, lease or convey all or substantially all of our assets to, or merge into, another business entity, unless:

Notwithstanding the foregoing, we may merge with another business entity or acquire by purchase or otherwise all or any part of the property or assets of any other company in a transaction in which we are the surviving entity.

Events of Default

Unless otherwise specified in any applicable prospectus supplement, the following are events of default with respect to any series of debt securities issued under the indenture:

If an event of default occurs and continues, then upon written notice to us, the trustee or the holders of at least 25% in principal amount of the outstanding debt securities of that series may declare the unpaid principal amount of and any accrued and unpaid interest on, all debt securities of that series to be due and payable immediately. However, at any time after a declaration of acceleration with respect to debt securities of any series has been made, the holders of a majority in principal amount of the outstanding debt securities of that series may rescind and annul the acceleration:

The indenture will provide that, subject to the duty of the trustee during an event of default to act with the required standard of care, the trustee will be under no obligation to exercise any of its rights or powers under the indenture

at the request or direction of any of the holders, unless the holders shall have offered to the trustee reasonable security or indemnity. Subject to certain provisions, including those requiring security or indemnification of the trustee, the holders of a majority in principal amount of the outstanding debt securities of any series will have the right to direct the time, method and place of conducting any proceeding for any remedy available to the trustee, or exercising any trust or power conferred on the trustee, with respect to the debt securities of that series.

We will be required to furnish to the trustee under the indenture annually a statement as to the performance by us of our obligations under that indenture and as to any default in our performance.

Modification of Indenture; Waiver

Subject to certain exceptions, the terms of the indenture or the debt securities may be amended or supplemented by us and the trustee with the written consent of the holders of at least a majority in principal amount of the outstanding debt securities of each series affected by the amendment with each series voting as a separate class. Without the consent of any holder of the debt securities, we and the trustee may amend the terms of the indenture or the debt securities to:

However, holders of each series of debt securities affected by a modification must consent to modifications that:

Any existing default may be waived with the consent of the holders of at least a majority in principal amount of the then outstanding debt securities of the series affected. The consent of the holders of debt securities is not necessary to approve the particular form of any proposed amendment to any indenture. It is sufficient if any consent approves the substance of the proposed amendment.

Covenants

Except as permitted in certain circumstances as discussed under "Consolidation, Merger or Sale," the indenture will require us to do or cause to be done all things necessary to preserve and keep in full force and effect our existence, rights (declaration and statutory) and franchises; provided, however, that we shall not be required to preserve any right or franchise if we determine that the right or franchise is no longer desirable in the conduct of our business and that the loss of the right or franchise is not disadvantageous in any material respect to the holders of the debt securities.

The indenture will require us to pay or discharge or cause to be paid or discharged, before payment becomes delinquent, all taxes, assessments and governmental charges levied or imposed upon us, except any tax, assessment, charge or claim the amount or applicability of which is being contested in good faith.

Reference is made to the indenture and any applicable prospectus supplement for information with respect to any additional covenants specific to a particular series of debt securities.

Discharge

Except as otherwise set forth in any applicable prospectus supplement, we may terminate our obligations under the debt securities of any series, and the corresponding obligations under the indenture when:

In addition, we will have the option to terminate substantially all our obligations under the debt securities of any series and the corresponding obligations under the indenture, and we may exercise that option if:

We will have the option to be released from our obligations with respect to the covenants to deliver reports required to be filed with the SEC and an annual compliance certificate, and to make timely payments of taxes (including covenants described in any applicable prospectus supplement), and any event of default occurring because of a default with respect to the covenants as they related to any series of debt securities, and we may exercise that option if:

Upon satisfaction of the applicable conditions, our obligations under the indenture with respect to the debt securities of the series, other than with respect to the covenants and events of default referred to above, shall remain in full force and effect.

Notwithstanding the foregoing, no discharge or defeasance described above shall affect the following obligations to or rights of the holders of any series of debt securities:

Form, Exchange and Transfer

We expect payment of principal, premium, if any, and any interest on the debt securities to be payable, and the exchange and the transfer of debt securities will be registrable, at the office of the trustee or at any other office or agency we maintain for that purpose. We expect to issue debt securities in denominations of U.S. $1,000 or integral multiples of $1,000. No service charge will be made for any registration of transfer or exchange of the debt securities, but we may require a payment to cover any tax or other governmental charges payable in connection with an exchange or transfer.

A holder of debt securities may transfer or exchange those debt securities in accordance with the indenture. The registrar for the debt securities may require a holder, among other things, to furnish appropriate endorsements and transfer documents, and to pay any taxes and fees required by law or permitted by the indenture. The registrar is not required to transfer or exchange any debt security selected for redemption or any debt security for a period of 15 days before a selection of debt security to be redeemed. The registered holder of a debt security may be treated as the owner of the security for all purposes.

We will name in any applicable prospectus supplement the security registrar, and any transfer agent in addition to the security registrar, that we initially designate for any debt securities. We may at any time designate additional transfer agents or rescind the designation of any transfer agent or approve a change in the office through which any transfer agent acts, except that we will be required to maintain a transfer agent in each place of payment for the debt securities of each series.

Replacement Securities

Any mutilated certificate representing a debt security or a certificate representing a debt security with a mutilated coupon will be replaced by us at the expense of the holder upon surrender of the certificate to the trustee. Certificates representing debt securities or coupons that become destroyed, stolen or lost will be replaced by us at the expense of the holder upon delivery to us and the trustee of evidence of any destruction, loss or theft satisfactory to us and the trustee, provided that neither we nor the trustee has been notified that the certificate or coupon has been acquired by a bona fide purchaser. In the case of any coupon which becomes destroyed, stolen or lost, the coupon will be replaced by issuance of a new certificate representing the debt security in exchange for the certificate representing the debt security to which the coupon appertains. In the case of a destroyed, lost or stolen certificate representing the debt security or coupon, an indemnity bond satisfactory to the trustee and us may be required at the expense of the holder of the debt security before a replacement certificate will be issued.

Information Concerning the Trustee

We will identify in any applicable prospectus supplement relating to any series of debt securities the trustee with respect to the series. The indenture and the Trust Indenture Act contain certain limitations on the rights of the trustee, should it become our creditor, to obtain payment of claims in certain cases, or to realize on certain property received in respect of any the claim, as security or otherwise. The trustee and its affiliates may engage in, and will be permitted to continue to engage in, other transactions with us and our affiliates, but if the trustee acquires any conflicting interest, as defined in the Trust Indenture Act, it must eliminate the conflict or resign.

The holders of a majority in principal amount of the then outstanding debt securities of any series will have the right to direct the time, method and place of conducting any proceeding for exercising any remedy available to the trustee. The Trust Indenture Act and the indenture provide that in case an event of default occurs is continuing, the trustee will be required, in the exercise of its rights and powers, to use the degree of care and skill of a prudent man in the conduct of his own affairs. Subject to those provisions, the trustee will be under no obligation to exercise any of its rights or powers under the indenture at the request of any of the holders of the debt securities, unless they have offered to the trustee indemnity satisfactory to it.

Global Debt Securities

Unless we indicate otherwise in any applicable prospectus supplement, the following provisions will apply to all debt securities.

The debt securities of a series may be issued in whole or in part in the form of one or more global securities that will be deposited with a depositary that we will identify in any applicable prospectus supplement. Each global security will be deposited with the depositary and will bear a legend regarding any related restrictions or other matters as may be provided for pursuant to the applicable indenture.

Unless any applicable prospectus supplement states otherwise, no global security may be transferred to, or registered or exchanged for, debt securities registered in the name of, any person or entity other than the depositary, unless:

All debt securities issued in exchange for a global security or any portion of a global security will be registered in those names as the depositary may direct. The specific terms of the depositary arrangement with respect to any portion of a series of debt securities to be represented by a global security will be described in any applicable prospectus supplement.

Debt securities which are to be represented by a global security to be deposited with or on behalf of a depositary will be represented by a global security registered in the name of the depositary or its nominee. Upon the issuance of the global security, and the deposit of the global security with the depositary, the depositary will credit, on its book-entry registration and transfer system, the respective principal amounts of the debt securities represented by the global security to the accounts of institutions that have accounts with the depositary or its nominee, or the Participants. The accounts to be credited will be designated by the underwriters or agents of the debt securities or by us, if the debt securities are offered and sold directly by us.

Ownership of beneficial interests in a global security will be limited to Participants or persons that may hold interests through Participants. Ownership of beneficial interests in a global security will be shown on, and the transfer of that ownership interest will be effected only through, records maintained by the depositary or its nominee for the global security or by Participants or persons that hold through Participants.

The laws of some jurisdictions require that certain purchasers of securities take physical delivery of the securities in certificated form. Those laws may impair the ability to transfer beneficial interests in global securities.

So long as the depositary, or its nominee, is the registered owner of a global security, the depositary or the nominee, as the case may be, will be considered the sole owner or holder of the debt securities represented by the global security for all purposes under the indenture. Payment of principal of, and premium and interest, if any, on debt securities will be made to the depositary or its nominee as the registered owner or bearer as the case may be of the

global security representing the debt securities. Each person owning a beneficial interest in a global security must rely on the procedures of the depositary and, if the person is not a Participant, on the procedures of the Participant through which the person owns its interest, to exercise any rights of a holder under the indenture. If we request any action of holders or if an owner of a beneficial interest in a global security desires to give any notice or take any action a holder is entitled to give or take under the indenture, the depositary will authorize the Participants to give the notice or take the action, and Participants would authorize beneficial owners owning through the Participants to give the notice or take the action or would otherwise act upon the instructions of beneficial owners owning through them.

The rights of any holder of a debt security to receive payment of principal and premium of, if any, and interest, on or after the respective due dates expressed or provided for in the debt security, or to institute suit for the enforcement of any payment on or after the applicable date, shall not be impaired or affected without the consent of the holders.

Neither we, the trustee, any paying agent nor the security registrar for a debt security will have any responsibility or liability for any aspect of the records relating to or payments made on account of beneficial ownership interests of the global security for the debt security or for maintaining, supervising or receiving any records relating to the beneficial ownership interests.

We expect that the depositary or its nominee, upon receipt of any payment of principal, premium or interest, will credit immediately Participants' accounts with payments in amounts proportionate to their respective beneficial interests in the principal amount of the global security as shown on the records of the depositary or its nominee. We also expect that payments by Participants to owners of beneficial interests in a global security held through the Participants will be governed by standing instructions and customary practices, as is now the case with securities held for the accounts of customers in bearer form or registered in "street name," and will be the responsibility of the Participants.

If the depositary for a global security representing debt securities of a particular series is at any time unwilling or unable to continue as depositary and we do not appoint a successor depositary within 90 days, we will issue debt securities of the series in definitive form in exchange for the global security. In addition, we may at any time and in our sole discretion determine not to have the debt securities of a particular series represented by one or more global securities and, in that event, will issue debt securities of the series in definitive form in exchange for all of the global securities representing debt securities of the series.

Payment and Paying Agents

Unless we otherwise indicate in any applicable prospectus supplement, we will make payment of the interest on any debt securities on any interest payment date to the person in whose name the debt securities, or one or more predecessor securities, are registered at the close of business on the regular record date for the interest.

We will pay principal of and any premium and interest on the debt securities of a particular series at the office of the paying agents designated by us, except that unless we otherwise indicate in any applicable prospectus supplement, we will make interest payments by check that we will mail to the holder or by wire transfer to certain holders. Unless we otherwise indicate in any applicable prospectus supplement, we will designate the corporate trust office of the trustee as our sole paying agent for payments with respect to debt securities of each series. We will name in any applicable prospectus supplement any other paying agents that we initially designate for the debt securities of a particular series. We will maintain a paying agent in each place of payment for the debt securities of a particular series.

All money we pay to a paying agent or the trustee for the payment of the principal of or any premium or interest on any debt securities that remains unclaimed at the end of two years after such principal, premium or interest has become due and payable will be repaid to us, and the holder of the debt security thereafter may look only to us for payment thereof.

Governing Law

The indenture and the debt securities will be governed by and construed in accordance with the internal laws of the State of New York, except to the extent that the Trust Indenture Act is applicable.

DESCRIPTION OF OTHER SECURITIES

We will set forth in any applicable prospectus supplement a description of any warrants or units issued by us that may be offered and sold pursuant to this prospectus.

SELLING STOCKHOLDERS

Information about selling stockholders, where applicable, will be set forth in a prospectus supplement, in a post-effective amendment or in filings we make with the SEC under the Exchange Act that are incorporated by reference.

PLAN OF DISTRIBUTION

We or any of the selling stockholders may sell the securities offered by this prospectus in any one or more of the following ways from time to time pursuant to:

The securities may be distributed from time to time in one or more transactions:

We will identify the specific plan of distribution, including any underwriters, dealers, agents or direct purchasers and their compensation in any applicable prospectus supplement.

LEGAL MATTERS

K&L Gates LLP, Irvine, California, will pass upon certain legal matters relating to the issuance and sale of the securities offered hereby on our behalf. Additional legal matters may be passed upon for us, the selling stockholders or any underwriters, dealers or agents, by counsel that we will name in the applicable prospectus supplement.

EXPERTS

The consolidated financial statements of ACM Research, Inc. at December 31, 2023, and for the year then ended, appearing in ACM Research, Inc.'s Annual Report on Form 10-K for the year ended December 31, 2023, and the effectiveness of ACM Research, Inc.'s internal control over financial reporting as of December 31, 2023, have been audited by Ernst & Young Hua Ming LLP, independent registered public accounting firm, as set forth in their reports thereon, included therein, and incorporated herein by reference. Such consolidated financial statements are incorporated herein by reference in reliance upon such reports given on the authority of such firm as experts in accounting and auditing.

The consolidated financial statements of ACM Research, Inc. for the year ended December 31, 2022, appearing in ACM Research, Inc.'s Annual Report on Form 10-K for the year ended December 31, 2023, have been audited by Armanino LLP, ACM Research, Inc.'s prior independent registered public accounting firm, as set forth in their report thereon, included therein, and incorporated herein by reference. Such consolidated financial statements are incorporated herein by reference in reliance upon such report given on the authority of such firm as experts in accounting and auditing.

The consolidated financial statements of ACM Research, Inc. for the year ended December 31, 2021, appearing in ACM Research, Inc.'s Annual Report on Form 10-K for the year ended December 31, 2023, have been audited by BDO China Shu Lun Pan Certified Public Accountants LLP, ACM Research, Inc.'s prior independent registered public accounting firm, as set forth in their report thereon, included therein, and incorporated herein by reference. Such consolidated financial statements are incorporated herein by reference in reliance upon such report given on the authority of such firm as experts in accounting and auditing.

WHERE YOU CAN FIND MORE INFORMATION

Available Information

We file reports, proxy statements and other information with the SEC. The SEC maintains a website at www.sec.gov that contains reports, proxy and information statements and other information about issuers, such as us, who file electronically with the SEC.

Our website address is www.acmrcsh.com. The information on our website, however, is not, and should not be deemed to be, a part of this prospectus or any prospectus supplement. We have included our website address as an inactive textual reference only. Through our website, we make available, free of charge, annual, quarterly and current reports, proxy statements, along with amendments thereto, and other information as soon as reasonably practicable after they are electronically filed with, or furnished to, the SEC.

This prospectus and any prospectus supplement are part of a registration statement that we filed with the SEC and do not contain all of the information in the registration statement. The full registration statement may be obtained from the SEC or us, as provided below. Forms of the indenture and other documents establishing the terms of the offered securities are or may be filed as exhibits to the registration statement or documents incorporated by reference in the registration statement. Statements in this prospectus or any prospectus supplement about these documents are summaries and each statement is qualified in all respects by reference to the document to which it refers. You should refer to the actual documents for a more complete description of the relevant matters. You may inspect a copy of the registration statement through the SEC's website, as provided above.

INCORPORATION BY REFERENCE

The SEC's rules allow us to "incorporate by reference" information into this prospectus, which means that we can disclose important information to you by referring you to another document filed separately with the SEC. The information incorporated by reference is deemed to be part of this prospectus, and subsequent information that we file with the SEC will automatically update and supersede that information. Any statement contained in this prospectus or a previously filed document incorporated by reference will be deemed to be modified or superseded for purposes of this prospectus to the extent that a statement contained in this prospectus or a subsequently filed document incorporated by reference modifies or replaces that statement.

We incorporate by reference our documents listed below and any future filings made by us with the SEC under Section 13(a), 13(c), 14 or 15(d) of the Exchange Act between the date of this prospectus and the termination of the offering of the securities described in this prospectus. We are not, however, incorporating by reference any documents or portions thereof, whether specifically listed below or filed in the future, that are not deemed "filed" with the SEC, including any Compensation Committee report and performance graph or any information furnished pursuant to Item 2.02 or 7.01 of Form 8-K or related exhibits furnished pursuant to Item 9.01 of Form 8-K.

This prospectus and any accompanying prospectus supplement incorporate by reference the documents set forth below that have previously been filed with the SEC:

All reports and other documents we subsequently file pursuant to Section 13(a), 13(c), 14 or 15(d) of the Exchange Act prior to the termination of this offering, including all such documents we may file with the SEC after the date of the initial registration statement and prior to the effectiveness of the registration statement, but excluding any information furnished to, rather than filed with, the SEC, will also be incorporated by reference into this prospectus and deemed to be part of this prospectus from the date of the filing of such reports and documents.

You may request a free copy of any of the documents incorporated by reference in this prospectus by writing or telephoning us at the following address:

ACM Research, Inc.

42307 Osgood Road, Suite I

Fremont, California

(510) 445-3700

Attention: Investor Relations

Exhibits to the filings will not be sent, unless those exhibits have been specifically incorporated by reference in this prospectus or any accompanying prospectus supplement.

 

2,884,615 Shares of Class A Common Stock

PROSPECTUS SUPPLEMENT

May 12, 2026