Exhibit 5.1

 

		801 Jefferson Avenue, Suite 300
		Redwood City, California 94063
		Tel: +1.650.328.4600 Fax: +1.650.463.2600
		www.lw.com
		FIRM / AFFILIATE OFFICES
		Austin		Milan
		Beijing		Munich
		Boston		New York
		Brussels		Orange County
		Chicago		Paris
		Dubai		Riyadh
May 13, 2026		Düsseldorf		San Diego
		Frankfurt		San Francisco
		Hamburg		Seoul
PDF Solutions, Inc.		Hong Kong		Silicon Valley
2858 De La Cruz Boulevard		Houston		Singapore
Santa Clara, California 95050		London		Tel Aviv
		Los Angeles		Tokyo
		Madrid		Washington, D.C.

 

Re:	Registration Statement on Form S-3

To the addressees set forth above:

We have acted as special counsel to PDF Solutions, Inc., a Delaware corporation (the “Company”), in connection with its filing on the date hereof with the Securities and Exchange Commission (the “Commission”) of a registration statement on Form S-3 (as amended, the “Registration Statement”), including a base prospectus (the “Base Prospectus”), which provides that it will be supplemented by one or more prospectus supplements (each such prospectus supplement, together with the Base Prospectus, a “Prospectus”), under the Securities Act of 1933, as amended (the “Act”), relating to the registration (a) for issue and sale by the Company of shares of the Company’s common stock, $0.00015 par value per share (the “Common Stock”), and (b) of shares of Common Stock to be resold from time to time by certain securityholders of the Company (the “Selling Securityholder Shares”). The Common Stock and the Selling Securityholder Shares are referred to herein collectively as the “Securities.”

This opinion is being furnished in connection with the requirements of Item 601(b)(5) of Regulation S-K under the Act, and no opinion is expressed herein as to any matter pertaining to the contents of the Registration Statement or related applicable Prospectus, other than as expressly stated herein with respect to the issue of the Securities.

As such counsel, we have examined such matters of fact and questions of law as we have considered appropriate for purposes of this letter. With your consent, we have relied upon certificates and other assurances of officers of the Company and others as to factual matters without having independently verified such factual matters. We are opining herein as to the General Corporation Law of the State of Delaware and we express no opinion with respect to the applicability thereto, or the effect thereon, of the laws of any other jurisdiction or, in the case of Delaware, any other laws, or as to any matters of municipal law or the laws of any local agencies within any state.

May 13, 2026

Page 2

 

 

Subject to the foregoing and the other matters set forth herein, it is our opinion that, as of the date hereof:

 

1.

When an issuance of Common Stock has been duly authorized by all necessary corporate action of the Company, upon issuance, delivery and payment therefor in an amount not less than the par value thereof in the manner contemplated by the applicable Prospectus and by such corporate action, and in total amounts and numbers of shares that do not exceed the respective total amounts and numbers of shares (a) available under the Company’s Third Amended and Restated Certificate of Incorporation, as amended (the “Certificate of Incorporation”), and (b) authorized by the board of directors in connection with the offering contemplated by the applicable Prospectus, such shares of Common Stock will be validly issued, fully paid and nonassessable. In rendering the foregoing opinion, we have assumed that the Company will comply with all applicable notice requirements regarding uncertificated shares provided in the General Corporation Law of the State of Delaware.

 

2.

When an issuance of Selling Securityholder Shares has been duly authorized by all necessary corporate action of the Company, upon issuance, delivery and payment therefor in an amount not less than the par value thereof in the manner contemplated by such corporate action, and in total amounts and numbers of shares that do not exceed the respective total amounts and numbers of shares (a) available under the Certificate of Incorporation and (b) authorized by the board of directors in connection with the issuance of such Selling Securityholder Shares, such Selling Securityholder Shares will be validly issued, fully paid and nonassessable. In rendering the foregoing opinion, we have assumed that the Company will comply with all applicable notice requirements regarding uncertificated shares provided in the General Corporation Law of the State of Delaware.

Our opinions are subject to:

 

(i)

the effects of bankruptcy, insolvency, reorganization, preference, fraudulent transfer, moratorium or other similar laws relating to or affecting the rights and remedies of creditors; and

 

(ii)

(a) the effects of general principles of equity, whether considered in a proceeding in equity or at law (including the possible unavailability of specific performance or injunctive relief), (b) concepts of materiality, reasonableness, good faith and fair dealing, and (c) the discretion of the court before which a proceeding is brought.

This opinion is for your benefit in connection with the Registration Statement and may be relied upon by you and by persons entitled to rely upon it pursuant to the applicable provisions of the Act. We consent to your filing this opinion as an exhibit to the Registration Statement and to the reference to our firm contained in the Prospectus under the heading “Legal Matters.” In giving such consent, we do not thereby admit that we are in the category of persons whose consent is required under Section 7 of the Act or the rules and regulations of the Commission thereunder.