EXHIBIT 8.1 [LETTERHEAD] March 10, 1997 KLA Instruments Corporation 160 Rio Robles San Jose, California 95134 Ladies and Gentlemen: We have acted as counsel for KLA Instruments Corporation, a Delaware corporation ("KLA") in connection with the preparation and execution of the Agreement and Plan of Reorganization dated as of January 14, 1997 (the "Reorganization Agreement") by and among KLA, Tiger Acquisition Corp., a wholly-owned subsidiary of KLA incorporated in California ("Merger Sub"), and Tencor Instruments, a California corporation ("Tencor"). Pursuant to the Reorganization Agreement, Merger Sub will merge with and into Tencor (the "Merger"), and Tencor will become a wholly-owned subsidiary of KLA. Unless otherwise defined, capitalized terms referred to herein have the meanings set forth in the Reorganization Agreement. All section references, unless otherwise indicated, are to the Internal Revenue Code of 1986, as amended (the "Code"). You have requested our opinion regarding certain United States federal income tax consequences of the Merger. In delivering this opinion, we have reviewed and relied upon the facts, statements, descriptions and representations set forth in the Reorganization Agreement (including Exhibits), the Registration Statement on Form S-4 filed with the Securities and Exchange Commission and such other documents pertaining to the Merger as we have deemed necessary or appropriate. We have also relied upon certificates of officers of KLA and Tencor, respectively (the "Officers' Certificates") and representations made by the shareholders of Tencor in "Affiliate Agreements." In connection with rendering this opinion, we have also assumed (without any independent investigation) that: 1. Original documents (including signatures) are authentic, documents submitted to us as copies conform to the original documents, and there has been (or will be by the Effective Time) due execution and delivery of all documents where due execution and delivery are prerequisites to effectiveness thereof; 2. Any statement made in any of the documents referred to herein,"to the best of the knowledge" of any person or party is correct without such qualification; KLA Instruments Corporation March 10, 1997 Page 2 3. All statements, descriptions and representations contained in any of the documents referred to herein or otherwise made to us are true and correct in all material respects and no actions have been (or will be) taken which are inconsistent with such representations; and 4. The Merger will be reported by KLA and Tencor on their respective federal income tax returns in a manner consistent with the opinion set forth below. 5. The Merger will be consummated pursuant to the Reorganization Agreement and will be effective under the law of the State of California. Based on our examination of the foregoing items and subject to the assumptions, exceptions, limitations and qualifications set forth herein, we are of the opinion that, if the Merger is consummated in accordance with the Reorganization Agreement (and without any waiver, breach or amendment of any of the provisions thereof) and the statements set forth in the Officers' Certificates and Affiliate Agreements are true and correct as of the Effective Time, then for federal income tax purposes; (a) The Merger will qualify as a "reorganization" within the meaning of Section 368(a) of the Code; and (b) The discussion entitled "Certain Federal Income Tax Considerations" in the Prospectus constituting a part of the Registration Statement insofar as it relates to statements of law or legal conclusions, is correct in all material requests. This opinion represents and is based upon our best judgment regarding the application of federal income tax laws arising under the Code, existing judicial decisions, administrative regulations and published rulings and procedures. Our opinion is not binding upon the Internal Revenue Service or the courts, and there is no assurance that the Internal Revenue Service will not successfully assert a contrary position. Furthermore, no assurance can be given that future legislative, judicial or administrative changes, on either a prospective or retroactive basis, would not adversely affect the accuracy of the conclusions stated herein. Nevertheless, we undertake no responsibility to advise you of any new developments in the application or interpretation of the federal income tax laws. This opinion addresses only the classification of the Merger as a reorganization under Section 368(a) of the Code, and does not address any other federal, state, local or foreign tax consequences that may result from the Merger or any other transaction (including any transaction undertaken in connection with the Merger). No opinion is expressed as to any transaction other than the Merger as described in the Reorganization Agreement or to any transaction whatsoever, including the Merger, if all the transactions described in the Reorganization Agreement are not consummated in accordance with the terms of such Reorganization Agreement and without waiver or breach of any material provision thereof or if all of the representations, warranties, statements and assumptions upon which we relied are not true and accurate at all relevant times. In the event any one of the statements, representations, KLA Instruments Corporation March 10, 1997 Page 3 warranties or assumptions upon which we have relied to issue this opinion is incorrect, our opinion might be adversely affected and may not be relied upon. This opinion has been delivered to you for the purpose of satisfying the requirements of Section 6.1(d) of the Reorganization Agreement. It may not be relied upon for any other purpose or by any other person or entity, and may not be made available to any other person or entity without our prior written consent. We hereby consent to the filing of this opinion as an exhibit to the Registration Statement. In giving this consent, however, we do not admit that we are in the category of persons whose consent is required under Section 7 of the Securities Act of 1933, as amended. Very truly yours, WILSON SONSINI GOODRICH & ROSATI Professional Corporation /s/ Wilson Sonsini Goodrich & Rosati