The numerical analysis of electromagnetic wave interaction in multi-layered media problems is important for a variety of applications such as microstrip antennas, microwave integrated circuits (MICs), geophysical prospecting modeling. Mixed potential integral equations (MPIEs) are usually used to analyze multi-layered media which results in the need of spatial Green's functions of the problem. The spectral Green's functions of the problem are analytically calculated using transmission line theory. However, the spatial Green's functions are given in terms of Sommerfeld integrals (SIs) which can not be evaluated in closed form. Numerical techniques have difficulties in accurately evaluating the Sommerfeld integrals due to the highly oscillatory and slowly converging behavior of the integrand. In this research, a new technique based on the expansion wave concept is developed to evaluate efficiently the Sommerfeld integrals arising from the muti-layered media. The annihilation of the asymptote and the branch-point singular behavior of the spectral Green's function is used in this technique. The contributions of the subtracted asymptotic and singularity terms are calculated analytically. The annihilation results in a remaining integral that is very smooth and can be calculated adaptively by using Gaussian quadratures to accelerate the convergence of the oscillating integrand. The accuracy and efficiency of the technique have been verified via representative numerical examples. Keywords: Multi-layered media; Green's function; microstrip structures; Sommerfeld integrals; expansion wave concept (EWC).