Abstract. For a lifted nontrivial additive character A' and a multiplicative character A of the finite field with q 2 elements, the "Gauss" sums SA'(trg) over g &SU(2n,q 2 ) and 2 A(detg)A'(trg) over g e U(2n,q 2 ) are considered. We show that the first sum is a polynomial in q with coefficients involving averages of "bihyperkloosterman sums" and that the second one is a polynomial in q with coefficients involving powers of the usual twisted Kloosterman sums. As a consequence, we can determine certain "generalized Kloosterman sums over nonsingular Hermitian matrices", which were previously determined by J. H. Hodges only in the case that one of the two arguments is zero.