We study the small data Cauchy problem for semilinear generalized Tricomi equations with nonlinear term of derivative type:Blow-up result and lifespan estimate from above are established for 1 < p ≤ 1 + 2 (m+1)(n−1)−m . If m = 0, our result coincides with that of the semilinear wave equation. The novelty is that we construct a new test function by using cutoff functions, the modified Bessel function and a harmonic function. We also find a interesting phenomenon: if n = 2, the blow-up power is independent of m.