[LETTERHEAD]
                                                                     EXHIBIT 5.1





                                March 10, 1997

KLA Instruments Corporation
160 Rio Robles
San Jose, CA 95134

         RE:  REGISTRATION STATEMENT ON FORM S-4

Ladies and Gentlemen:

         We have examined the Registration Statement on Form S-4 to be filed by
you with the Securities and Exchange Commission on or about this date (the
"Registration Statement"), in connection with the registration under the
Securities Act of 1933, as amended, of shares of your Common Stock, par value
$0.001 per share (the "Shares").   As your legal counsel in connection with
this transaction, we have examined the proceedings taken and are familiar with
the proceedings proposed to be taken by you in connection with the sale and
issuance of the Shares.

         It is our opinion that upon conclusion of the proceedings being taken
or contemplated by us, as your counsel, to be taken prior to the issuance of
the Shares, and upon completion of the proceedings being taken in order to
permit such transactions to be carried out in accordance with the securities
laws of the various states where required, the Shares, when issued and sold in
the manner described in the Registration Statement, 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, including the Joint Proxy Statement/Prospectus
constituting a part thereof, and any amendment thereto.

                                        Sincerely,

                                        WILSON SONSINI GOODRICH & ROSATI
                                        Professional Corporation

                                        /s/ Wilson Sonsini Goodrich & Rosati