EXHIBIT 10.26 December 18, 1998 Mr. Larry Gerhard Summit Design, Inc. 9305 S.W. Gemini Drive Beaverton, OR 97008 RE: Software OEM License Agreement between Summit Design, Inc. (SDI) and Credence Systems Corporation (CSC) dated July 11, 1997 ("OEM Agreement") Dear Larry: The OEM agreement provides for a maximum shipment of VTB licenses by SDI in each quarter. CSC hereby requests the following change in the Schedule D License Fee and Payment: Quarterly Maximum Shipments Current Requested ------- --------- Q4 1998 Licenses at * * * Q1 1999 Licenses at * * * Q2 1999 Licenses at * * * Q3 1999 Licenses at * * * Q4 1999 Licenses at * * * --- --- Total * * --- --- CSC will authorize payment one day after shipment of licenses provided that SDI agrees that the OEM Agreement is thereby terminated with no restrictions on any subsequent use, sale, license or distribution of the VTB Software purchased by CSC under the OEM Agreement. Sincerely, /s/ Jerry Bruce Jerry Bruce Vice President, Treasurer and Corporate Controller Credence Systems Corporation Agreed: /s/ Larry J. Gerhard - ------------------------------------- Larry J. Gerhard * Certain information on this page has been omitted and filed separately with the Commission. Confidential treatment has been requested with respect to the omitted portions.