UNITED STATES SECURITIES AND EXCHANGE COMMISSION

FORM 10-K/A

Amendment No. 1 to Form 10-K

For the transition period from                     to                    

000-31311
(Commission file number)

(408) 280-7900
(Registrant’s telephone number, including area code)

Securities registered pursuant to Section 12(b) of the Act:

Securities registered pursuant to Section 12(g) of the Act:

Common Stock, $0.00015 par value

Indicate by check mark whether the Registrant (1) has filed all reports required to be filed by Section 13 or 15(d) of the Securities Act of 1934 during the preceding 12 months (or for such shorter period that the Registrant was required to file such reports), and (2) has been subject to such filing requirements for the past 90 days. Yes þ No o

Indicate by check mark if disclosure of delinquent filers pursuant to Item 405 of Regulation S-K is not contained herein, and will not be contained, to the best of registrant’s knowledge, in definitive proxy or information statements incorporated by reference in Part III of this Form 10 K or any amendment to this Form 10 K. þ

Indicate by check mark whether the registrant is an accelerated filer (as defined in Exchange Act Rule 12b-2). Yes þ No o

The aggregate market value of the voting stock held by non-affiliates of the Registrant was approximately $121,150,177 as of the last business day of the Registrant’s most recently completed second quarter, based upon the closing sale price on the Nasdaq National Market reported for such date. Shares of Common Stock held by each officer and director and by each person who owns 5% or more of the outstanding Common Stock have been excluded in that such persons may be deemed to be affiliates. This determination of affiliate status is not necessarily a conclusive determination for other purposes.

There were 25,479,186 shares of the Registrant’s Common Stock issued and outstanding as of March 8, 2004.

DOCUMENTS INCORPORATED BY REFERENCE

Part III incorporates information by reference from the definitive Proxy Statement for our Annual Meeting of Stockholders to be held on May 19, 2004.

Table of Contents

EXPLANATORY NOTE

     PDF Solutions, Inc. (“PDF” or the “Company”) is filing this Amendment No. 1 on Form 10-K/A (this “Amendment”) to amend the Company’s Annual Report on Form 10-K for the year ended December 31, 2003, as filed with the Securities and Exchange Commission on March 15, 2004. Specifically, the purpose of this Amendment is to correct typographical errors in the certification of the principal executive officer and of the principal financial officer pursuant to section 302 of the Sarbanes-Oxley Act of 2002. This Amendment speaks as of the original filing date of PDF’s Annual Report on Form 10-K. Except for such exhibits, no other changes to the Annual Report on Form 10-K are being made by means of this filing.

SIGNATURES

     Pursuant to the requirements of Section 13 or 15(d) of the Securities Exchange Act of 1934, the Registrant has duly caused this report to be signed on its behalf by the undersigned, thereunto duly authorized.

INDEX TO EXHIBITS