EXHIBIT 5.1




                                  [Letterhead]


                                 August 7, 1998





KLA-Tencor Corporation
160 Rio Robles
San Jose, CA 95134

     RE: REGISTRATION STATEMENT ON FORM S-8

Ladies and Gentlemen:

     We have examined the Registration Statement on Form S-8 to be filed by you
with the Securities and Exchange Commission on or about August 7, 1998 (the
"Registration Statement"), in connection with the registration under the
Securities Act of 1933, as amended, of 300,000 shares of Common Stock (the
"Shares") reserved for issuance under the Excess Profit Stock Plan (the "Plan").
As your legal counsel, we have examined the proceedings taken and proposed to be
taken in connection with the issuance, sale and payment of consideration for the
Shares to be issued under the Plans.

     It is our opinion that, when issued and sold in compliance with applicable
prospectus delivery requirements and in the manner referred to in the Plans and
pursuant to the agreements which accompany the Plans, the Shares will be legally
and validly issued, fully paid and non-assessable.

     We consent to the use of this opinion as an exhibit to the Registration
Statement and further consent to the use of our name wherever appearing in the
Registration Statement and any amendments thereto.

                                         Sincerely,

                                         WILSON SONSINI GOODRICH & ROSATI
                                         Professional Corporation

                                         /s/ Wilson Sonsini Goodrich & Rosati
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