<PAGE>


                                                                   Exhibit 10.20

November 5, 2001


David Martin
2016 Stockbridge Ave.
Redwood City, CA  94061

Re:  Separation Agreement Including A General Release

Dear Dave:

     This letter sets forth the terms of our agreement with respect to your
separation from employment with RITA Medical Systems, Inc. ("RITA").

     Your final date of active employment with RITA will be November 5, 2001. As
of that date, except as specifically provided in this Agreement, you will not be
entitled to any compensation, including bonuses, and all other benefits and
perquisites of employment from RITA. In addition, as of November 5, 2001, you
are no longer authorized to incur any expenses on behalf of RITA.

     You may elect to continue your medical coverage at the prevailing active
employee rate(s) as provided by the Consolidated Omnibus Budget Reconciliation
Act of 1986 ("COBRA"). Additional information concerning your COBRA rights will
be provided separately.

     In addition to the above benefits to which you are entitled whether or not
you choose to accept the this Agreement, you are presently eligible for
additional compensation and benefits in exchange for a Release of Claims and
certain other agreements by you. To be eligible for additional compensation and
benefits, you must return a fully executed original of this Agreement as
described below and all RITA property in your possession, as described below, on
or before November 5, 2001. In the event that you choose to accept this
Agreement, return a fully executed original of this Agreement to me, and return
all RITA property on or before November 5, 2001, you will be entitled to the
following:

     (1)  Salary continuation payments in an amount equal to your regular salary
          (base, commission and car allowance) as of October 31, 2001 less
          authorized and required deductions; for a period of two months, from
          November 1, 2001 until December 31, 2001. These salary continuation


<PAGE>

          payments shall be paid in semi-monthly installments on RITA regular
          paydays.

     (2)  Continued vacation accrual and stock option vesting through December
          31, 2001.

     (3)  RITA will continue your health care benefits at the group rate through
          December 31, 2001. After December 31, 2001, you may elect to continue
          such coverage at your own expense and consistent with your rights and
          obligations under COBRA.

     (4)  A lump sum payment representing five additional months of base salary
          ($72,916.66, less authorized and required deductions), to be paid on
          December 31, 2001.

     (5)  An additional payment of up to two months base salary ($29,166.66,
          less authorized and required deductions), to be paid based on Q1 2002
          sales results as soon as such sales results are known (approximately
          April 5, 2002):

          -    If less than 90% of Q1 2002 budget achieved = $0

          -    If 90% or more of Q1 2002 budget achieved = (percentage achieved
               up to 100% x $29,166.66)

     (6)  A grant warrant of twenty five thousand (25,000) shares with a grant
          date and price marked as of RITA's stock price on October 26, 2001.
          The term of the warrant will be seventeen (17) months (giving 1 year
          to exercise after released from escrow at end of Q1 02). Shares shall
          be held in escrow until the end of Q1 02 and shall be released only if
          no RITA employees have been recruited to a new company by which you
          are employed or for which you provide consulting services during the
          period of time from ( ) to ( ).

     In return for the payments and other benefits described in numbered
paragraphs one through six above, which you acknowledge exceed the amount to
which you otherwise are entitled under RITA policies and practices, you (on
behalf of yourself, your spouse, heirs, agents and representatives) completely
release RITA and its present and former directors, officers, agents, affiliates,
successors, predecessors, assigns, managers and employees from all claims of any
kind, known and unknown, which you may now have or have ever had against RITA,
including claims for compensation, bonuses, severance pay, stock options, and
all claims arising from your employment with RITA or the termination of your
employment, whether based on contract, tort, statute, local


<PAGE>

ordinance, regulation or any comparable law in any jurisdiction ("Released
Claims"). By way of example and not in limitation, the Released Claims shall
include any claims arising under Title VII of the Civil Rights Act of 1964, the
Americans with Disabilities Act, and the California Fair Employment and Housing
Act, as well as any claims asserting wrongful termination, breach of contract,
breach of the covenant of good faith and fair dealing, negligent or intentional
infliction of emotional distress, negligent or intentional misrepresentation,
negligent or intentional interference with contract or prospective economic
advantage, and defamation.

     You agree that because these releases specifically cover known and unknown
claims, you waive your rights under Section 1542 of the California Civil Code,
or under any comparable law of any jurisdiction. Section 1542 states:

          "A general release does not extend to claims which the creditor does
          not know or suspect to exist in his favor at the time of executing the
          release, which if known by him must have materially affected his
          settlement with the debtor."

     You agree not to disclose any confidential, proprietary or know-how
belonging to RITA or acquired by you during your employment with RITA as
described in the Confidential Information And Invention Assignment Agreement
("Non-Disclosure Agreement"). You acknowledge that the Non-Disclosure Agreement
entered into by you on February 11, 2000 remains in effect after your employment
with RITA ends.

     You represent that you have returned all RITA property (including without
limitation, keys to all offices and facilities, mobile telephones, employee
handbooks, business cards, client files, corporate credit cards, telephone
calling cards, files, sales material) in your possession and you have not
retained any reproductions of these items.

     You understand and agree that this Agreement shall be maintained in strict
confidence, and that you shall not disclose this Agreement or any of its terms
to any other person other than your spouse, accountant, or attorney (all of whom
shall then be bound by the same agreement of confidentiality) or unless required
by law.

     The laws of the State of California shall govern this Agreement. You and
RITA further agree that any and all disputes arising out of the terms,
interpretation, application, or alleged breach of this Agreement shall be
subject to binding arbitration, which shall be conducted in Santa Clara County,
California, in accordance with the National Rules for the Resolution of
Employment Disputes of the American Arbitration Association, as amended. The
costs of the arbitration shall be borne by RITA unless otherwise permitted by
law. Notwithstanding any other provision of this Agreement, if any legal or
equitable action or arbitration is necessary to enforce the terms of this
Agreement, the prevailing


<PAGE>

party shall be entitled to a reasonable sum for attorneys' fees and costs and an
action for equitable relief only may be brought directly in the Superior Court
of California, in and for the County of Santa Clara, the court in which both
RITA and you agree that jurisdiction and venue for such equitable claims are
proper.

     You and RITA also agree that this letter contains all of our agreements and
understandings, and fully supersedes any prior agreements or understandings that
we may have had regarding the subject matter of this Agreement.

     Finally, by your signature below, you acknowledge each of the following:
(a) that you have read this Agreement or have been afforded every opportunity to
do so; (b) that you are fully aware of the Agreement's contents and legal
effect; and (c) that you have chosen to enter into this Agreement freely,
without coercion and based upon your own judgment and not in reliance upon any
promises made by RITA other than those contained in this letter.

     If this letter comports with your understanding of our Agreement, please
sign on the line provided below and return the original to Harriet Bell, HR
Director in a confidential envelope by November 5, 2001.

                                   Sincerely,

                                   /s/ Donald Stewart
                                   -------------------------------------
                                   Donald J. Stewart, CFO
                                   RITA Medical Systems, Inc.


     I have read and understand the Agreement above and agree to be bound by its
terms and conditions.

/s/ David Martin                                  11/5/01
---------------------------------                 ------------------------
David Martin                                      Date