Power metal semiconductor field effect transistors (MESFET'S) have been fabricated to show that they have come to the stage of practical use. This paper reviews what have inhibited the practical use of GaAs-on-Si electronic devices and how they have been overcome by focusing the application of GaAs-on-Si to the power MESFET's and high electron mobility transistors (HEMT's). It is demonstrated that the practical application of the GaAs-on-Si power MESFET's to the base-station devices for mobile phones is one of the most attractive in the very near future.