EXHIBIT 99.4

                            CERTIFICATION PURSUANT TO
                             18 U.S.C. SECTION 1350,
                             AS ADOPTED PURSUANT TO
                  SECTION 906 OF THE SARBANES-OXLEY ACT OF 2002

     In connection with the Quarterly Report of Knight Transportation, Inc. (the
"Company")  on Form 10-Q for the period ended June 30,  2003,  as filed with the
Securities and Exchange Commission on the date hereof (the "Report"), I, Timothy
M. Kohl, Chief Financial Officer of the Company,  certify, pursuant to 18 U.S.C.
Section 1350, as adopted  pursuant to Section 906 of the  Sarbanes-Oxley  Act of
2002, that to the best of my knowledge:

     (1)  The Report fully  complies with the  requirements  of Section 13(a) or
          15(d) of the Securities Exchange Act of 1934; and

     (2)  The  information  contained  in the  Report  fairly  presents,  in all
          material respects,  the financial  condition and results of operations
          of the Company.

                                        /s/ Timothy M. Kohl
                                        ----------------------------------------
                                        Timothy M. Kohl
                                        Chief Financial Officer
                                        July 25, 2003

A SIGNED  ORIGINAL OF THIS  WRITTEN  STATEMENT  REQUIRED BY SECTION 906 HAS BEEN
PROVIDED  TO  KNIGHT  TRANSPORTATION,  INC.  AND  WILL  BE  RETAINED  BY  KNIGHT
TRANSPORTATION,  INC. AND FURNISHED TO THE SECURITIES AND EXCHANGE COMMISSION OR
ITS STAFF UPON REQUEST.