Abstract: Optically controlled photoconductive semiconductor switches (PCSS's) have potential importance in generation of high power microwaves due to their unique advantages compared with traditional high power pulsed devices. Microwave can be generated directly from DC source by applying PCSS. The configuration of PCSS and their two operation modes are described in this paper, and the characteristics of the two modes also are presented. Various techniques for the generation of high power microwaves using PCSS are discussed.