In this article, we study semi-linear σ-evolution equations with double damping including frictional and visco-elastic damping for any σ ≥ 1. We are interested in investigating not only higher order asymptotic expansions of solutions but also diffusion phenomenon in the L p − L q framework, with 1. Introduction. In this paper, let us consider the following Cauchy problem for semi-linear σ-evolution equations with frictional and visco-elastic damping terms: u tt + (−∆) σ u + u t + (−∆) σ u t = |u| p , u(0, x) = u 0 (x), u t (0, x) = u 1 (x), (1) where σ ≥ 1 and a given real number p > 1. The corresponding linear equation with vanishing right-hand side is u tt + (−∆) σ u + u t + (−∆) σ u t = 0, u(0, x) = u 0 (x), u t (0, x) = u 1 (x). (2) At first, let us recall some recent results concerning the study of typical important problems of (1) and (2) with σ = 1, the so-called wave equations with frictional