The high-voltage ultra-fast photoconductive semiconductor switches（PCAS’s） fabricated with Si-GaAs coated by all-solid insulation protection technique are reported in this paper. The largesthold-off strength of 35 kV/cm of fabricated switches is obtained. We have used PCSS’s to switch voltage as high as 30 kV/cm and current about 100 A and preduced rise time as fast as 200 ps in the initiation of lock-on. Using all-solid technique to fabrication of high-voltage GaAs switch makes the device structure more simple and more practical.