To drive the high power klystrons used in electron accelerators in RRCAT we have undertaken an endeavor develop state of art solid state S-Band microwave amplifiers indigenously. High power amplifier in S –Band are not that easily available and are also quite costly. Indigenous development of amplifiers will not only reduce cost of microwave systems but also increase reliability and efficiency. Amplifier systems of up to 300 W in S-Band have been developed, a modular design approach has been used in which several gain stages matched to 50 ohms are utilized to provide high gain and power. Class C, S-Band pulsed power transistors are utilized for high power stages, for higher efficiency and ruggedness. These amplifiers have been used in microwave systems of the 10 MeV electron LINAC and 20 MeV injector Microtron.