EXHIBIT 5.1


            OPINION AND CONSENT OF ORRICK, HERRINGTON & SUTCLIFFE LLP

January 10, 2003


PDF Solutions, Inc.
333 West San Carlos Street, Suite 700
San Jose, California 95110

      Re:   PDF Solutions, Inc.
            Registration Statement on Form S-8



Ladies and Gentlemen:

      At your request, we are rendering this opinion in connection with the
Registration Statement on Form S-8 (the "Registration Statement") filed by you
with the Securities and Exchange Commission (the "Commission") on or about
January 10, 2003 in connection with the registration under the Securities Act of
1933, as amended, of a total of 3,221,622 shares of your Common Stock (the
"Common Shares") reserved for issuance under the PDF Solutions, Inc. 2001 Stock
Plan and the PDF Solutions, Inc. 2001 Employee Stock Purchase Plan.

      We have examined instruments, documents, and records which we deemed
relevant and necessary for the basis of our opinion hereinafter expressed. In
such examination, we have assumed the following: (a) the authenticity of
original documents and the genuineness of all signatures; (b) the conformity to
the originals of all documents submitted to us as copies; and (c) the truth,
accuracy, and completeness of the information, representations, and warranties
contained in the records, documents, instruments, and certificates we have
reviewed.

      Based on such examination, we are of the opinion that the Common Shares,
when issued and sold as described in the Registration Statement, will be legally
issued, fully paid and nonassessable.

      We hereby consent to the filing of this opinion as an exhibit to the
above-referenced Registration Statement and to the use of our name wherever it
appears in said Registration Statement, including the Prospectus constituting a
part thereof, as originally filed or as subsequently amended or supplemented. In
giving such consent, we do not consider that we are "experts" within the meaning
of such term as used in the Securities Act of 1933, as amended, or the rules and
regulations of the Securities and Exchange Commission issued thereunder, with
respect to any part of the Registration Statement, including this opinion as an
exhibit or otherwise.

Very truly yours,


/s/ ORRICK, HERRINGTON & SUTCLIFFE LLP