Exhibit 99.20

                          CREDENCE SYSTEMS CORPORATION
                               215 Fourier Avenue
                                Fremont, CA 94539




Dr. William G. Howard, Jr.

Dear Bill:

                  This letter agreement is intended to memorialize the terms and
conditions under which you have agreed to serve as the Chairman of the Company's
Board of Directors and for your services performed during the period the Company
is  engaged in the search for a new Chief  Executive  Officer.  Those  terms and
conditions may be summarized as follows:

1.   You will  assume your new  position as Chairman of the Board of  Directors,
     effective  December  8,  1998,  and  during  the  period  you serve in that
     capacity  prior  to  the  Board's  appointment  of a  new  permanent  Chief
     Executive Officer, you will have both executive officer and employee status
     with the Company.

2.   As an employee, your base salary will be $10,000 per month and will be paid
     in accordance with the Company's normal payroll  practices,  subject to the
     Company's   collection  of  all   applicable   income  and  employment  tax
     withholdings.  You will be reimbursed for all reasonable  expenses incurred
     in connection with your employment.

3.   You were  granted a stock  option on December  8, 1998 to  purchase  15,000
     shares of the Company's  common stock at an exercise  price of $19.8125 per
     share,  the closing selling price on December 8, 1998. The option will be a
     non-statutory  option  under the  federal  tax laws and will have a maximum
     term of ten (10) years,  subject to earlier termination upon your cessation
     of service with the Company as an employee, consultant or Board member. The
     option  will  become  exercisable  for all of the  option  shares  upon the
     earlier of (i) your completion of six (6) years of service with the Company
     measured  from  the  December  8,  1998  grant  date  or (ii)  the  Board's
     appointment of a new permanent Chief Executive Officer.

4.   During your period of employment with the Company, you will not be eligible
     to receive  any  compensation  payable to the  non-employee  members of the
     Board,  whether in the form of cash fees or automatic  option  grants under
     the Company's 1993 Stock Option Plan.

5.   You will be eligible to participate in all group term life insurance plans,
     group health plans, accidental death and dismemberment plans and short-term
     disability  programs  and  other  executive   perquisites  which  are  made
     available to the Company's  executives and for which you qualify.  You will
     accrue  paid  vacation  benefits  at the rate of one (1) week per  calendar
     quarter.


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6.   The executive  officer and employee  status of your position as Chairman of
     the Board is not for any specified period of time. As a result,  either you
     or the  Company  are  free to  terminate  that  status  at any time for any
     reason, with or without cause. In addition, your employment status with the
     Company will terminate  immediately  upon the Board's  appointment of a new
     Chief Executive Officer or upon your death or disability.  At the time your
     employment status terminates,  the Company will only be required to pay you
     (i) any unpaid base salary for services  rendered  through the date of such
     termination  and (ii) the dollar  value of all accrued and unused  vacation
     benefits  based upon the level of base salary in effect for you at the time
     of your termination. The termination of your executive officer and employee
     status will not affect  your  continuation  on the Board as a  non-employee
     director or as Chairman of the Board, if the Board so determines.

7.   This letter agreement  constitutes the full and complete  agreement between
     us  concerning  the  terms of your  service  as an  executive  officer  and
     employee of the Company in your capacity as Chairman of the Board. Although
     your duties, title,  compensation and/or benefits, as well as the Company's
     personnel  policies and  procedures,  may change from time to time, the "at
     will" nature of your  employment may only be changed by an express  written
     agreement signed by you and a duly authorized officer of the Company.

         To indicate your acceptance of the foregoing terms of your  employment,
please sign the acceptance paragraph below and return it to my attention.

                                Very truly yours,

                                /s/ Dennis Wolf_____________________


                                   ACCEPTANCE

                  I  hereby  accept  and  agree  to  the  terms  and  conditions
specified  above for my employment  with  Credence  Systems  Corporation  in the
executive officer position of Chairman of the Board.

                               /s/ Dr. William G. Howard, Jr.______
                               Dr. William G. Howard, Jr.

                               Dated:   March 31, 1999


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