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                                 EXHIBIT 10.66

             AMENDMENT OF CREDIT AGREEMENT BETWEEN BANK OF AMERICA
                NT & SA AND THE COMPANY DATED DECEMBER 31, 1993

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                     SEVENTH AMENDMENT TO CREDIT AGREEMENT


         This SEVENTH AMENDMENT TO CREDIT AGREEMENT (this Amendment"), dated as
of December 31, 1993, is entered into by and between KLA INSTRUMENTS
CORPORATION (the "Borrower") and BANK OF AMERICA NATIONAL TRUST AND SAVINGS
ASSOCIATION ("the Bank").


                                    Recitals

         A.    The Bank and the Borrower are parties to a Credit Agreement,
dated as OF November 15, 1991 (the "Original Credit Agreement"), as amended by
a Waiver and First Amendment, dated as of July 29, 1992, by a Second Amendment
to Credit Agreement, dated as of October 28, 1992, by a Third Amendment to
Credit Agreement, dated as of December 31, 1992, by a Fourth Amendment to
Credit Agreement, dated as of February 28, 1993, by a Fifth Amendment to Credit
Agreement, dated as of March 31, 1993, and by a Sixth Amendment to Credit
Agreement, dated as of June 1, 1993 (the Original Credit Agreement, as so
amended, is referred to herein as the "Credit Agreement"), pursuant to which
the Bank has extended certain credit facilities to the Borrower and certain of
its subsidiaries.

         B.    The Borrower has requested that the Bank extend this Credit
Agreement, as set forth in this Seventh Amendment.

         C.     The Bank is willing to amend the Credit Agreement subject to
the terms and conditions of this Amendment.


         NOW, THEREFORE, for valuable consideration, the receipt and adequacy
of which are hereby acknowledged, the parties hereto hereby agree as follows:


                 1.    Defined Terms.  Unless otherwise defined herein,
capitalized terms used herein shall have the meanings, if any, assigned to them
in the Credit Agreement.

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                 2.     Amendments to Credit Agreement.

                          (a)   The first sentence of Paragraph 1.1 of the
                 Credit Agreement is hereby amended by replacing the phrase
                 "December 31, 1993" with the phrase "March 31, 1994."

                          (b)   The sixth sentence of Paragraph 1.2(b) of the
                 Credit Agreement is hereby amended by replacing the phrase
                 "December 31, 1993" with the phrase "March 31, 1994."

                          (c)   The definition of the term "CD Rate Interest
                 Period" occurring in Paragraph 1.3 (g) of the Credit Agreement
                 is hereby amended by replacing the phrase "beyond June 30,
                 1994" with the phrase "beyond September 30, 1994."

                          (d)   The definition of the term "Offshore Rate
                 Interest Period" occurring in Paragraph 1.4 (f) of the Credit
                 Agreement is hereby amended by replacing the phrase "beyond
                 June 30, 1994" with the phrase "beyond September 30, 1994".

                          (e)   Paragraph 1.5 (d) of the Credit Agreement is
                 hereby amended by replacing the phrase "June 30, 1994" with
                 the phrase "December 31, 1994".

                          (f)   Section 1.6 (d) of the Credit Agreement is
                 hereby amended to read in full as follows: "No standby
                 letter of credit shall expire later than March 31, 1995."
                

                          (g)   The first sentence of Paragraph 1.9 of the
                 Credit Agreement is hereby amended by replacing the phrase
                 "December 31, 1993" with the phrase "March 31, 1994."

                          (h)   The second sentence of Paragraph 1.9 of the
                 Credit Agreement is hereby amended by replacing the phrase
                 "and the last period which shall end on December 31, 1993"
                 with the phrase "and the last period which shall end on March
                 31, 1994."

                          (i)   The third sentence of Paragraph 1.9 of the
                 Credit Agreement is hereby amended by replacing the phrase
                 "December 31, 1993" with the phrase "March 31, 1994." 



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                 3. Representations and Warranties.  The Borrower hereby
represents and warrants to the Bank as follows:

                          (a)   No Event of Default has occurred and is
                 continuing, and no event has occurred or condition exists
                 which with notice or the passage of time would become an Event
                 of Default..

                          (b)   The execution, delivery, and performance by the
                 Borrower of this Amendment have been duly authorized by all
                 necessary corporate and other action and do not and will not
                 require any registration with, consent or approval of, notice
                 to or action by, any person (including any governmental
                 agency) in order to be effective and enforceable.  The Credit
                 Agreement as amended by this Amendment constitutes the legal,
                 valid, and binding obligations of the Borrower, enforceable
                 against it in accordance with its respective terms,  without
                 defense, counterclaim or offset.

                         (c)   All representations and warranties of the
                 Borrower contained in the Credit Agreement are true and
                 correct.

                          (d)    The Borrower is entering into this Amendment
                 on the basis of its own investigation and for its own reasons,
                 without reliance upon the Bank or any other person.


                 4.     Effective Date.  This Amendment will become effective
as of December 31, 1993 (the" Effective Date") provided that each of the
following conditions precedent has been satisfied:

                        (a)       The Bank has received from the Borrower a
                 duly executed original of this Amendment.

                        (b)       All representations and warranties contained
                 herein are true and correct as of the Effective Date.
                                  


                 5.     Reservation of Rights.      The Borrower acknowledges
and agrees that the execution and delivery by the Bank of this Amendment shall
not be deemed to create a course of dealing or otherwise obligate the Bank to
forbear or execute similar amendments under the same or similar circumstances
in the future.

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                 6.    Miscellaneous.

                          (a)    Except as herein expressly amended, all terms,
                 covenants, and provisions of the Credit Agreement are and
                 shall remain in full force and effect and all references
                 therein to such Credit Agreement shall henceforth refer to the
                 Credit Agreement as amended by this Amendment.  This Amendment
                 shall be deemed incorporated into, and a part of, the Credit
                 Agreement.

                          (b)    This Amendment shall be binding upon and inure
                 to the benefit of the parties hereto and thereto and their
                 respective successors and assigns.  No third party
                 beneficiaries are intended in connection with this Amendment.

                          (c)   This Amendment shall be governed by and 
                 construed in accordance with the law of the State of
                 California.

                          (d)     This Amendment may be executed in any number
                 of counterparts, each of which shall be deemed an original,
                 but all such counterparts together shall  constitute but one
                 and the same instrument.

                          (e)    This Amendment, together with the Credit
                 Agreement, contains the entire and exclusive agreement of the
                 parties hereto with reference to the matters discussed herein
                 and therein.  This Amendment supersedes all prior drafts and
                 communications with respect thereto.  This Amendment may not
                 be amended except in writing executed by both of the parties
                 hereto.

                          (f)    If any term or provision of this Amendment
                 shall be deemed prohibited by or invalid under any applicable
                 law, such provision shall be invalidated without affecting the
                 remaining provisions of this Amendment or the Credit
                 Agreement, respectively.

                          (g)   The Borrower covenants to pay to or reimburse
                 the Bank, upon demand, for all costs and expenses ( including
                 allocated costs of in-house counsel) incurred in connection
                 with the development, preparation, negotiation, execution and
                 delivery of this Amendment, including without limitation
                 appraisal, audit, search and filing fees incurred in
                 connection therewith.

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         IN WITNESS WHEREOF, the parties hereto have executed and delivered
this Amendment as of the date first above written.


                          KLA INSTRUMENTS CORPORATION

                                   By:
                                   __________________________________________
                            
                                   Title:
                                   __________________________________________


                            
                                    BANK OF AMERICA NATIONAL TRUST
                                    AND SAVINGS ASSOCIATION

                                    By:
                                     _________________________________________
                                     Kevin McMahon, Vice President

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