The propagation mechanisms of radio waves over intra-chip channels was studied with integrated antennas for wireless chip area networks. Test vehicles were designed and fabricated on silicon wafers of both low and high resistivities, respectively, using complementary metal oxide semiconductor (CMOS) processes. On-wafer measurements for propagation of radio waves over intra-chip channels were conducted in the frequency domain from 10 to 110 GHz with a network analyzer. Time-domain analysis was performed to characterize intra-chip radio channels and more importantly to understand the propagation mechanisms. It was found that path loss factor is constantly less than two and propagation delay of the first-arrival wave is significantly longer than that by free-space transmission. Thus, we concluded that the propagation of radio waves over intra-chip channels is mainly realized with surface wave rather than space wave. Surface wave is guided on air-wafer interface. In addition, effects of metal lines, in both parallel and normal placements with respect to wave propagation direction, on signal propagation were also investigated.