The withstand voltage experiments are done with fabricated 3mm gap coplanar electrodes GaAs photoconductive semiconductor switch（PCSS）.The comparison between static insulation resistance

dark-current and withstand voltage are analyzed

and results show if a PCSS dark-current is less than or equal to 3μA at 1kV DC

the breakdown voltage in experiment is about 12kV

and this conclusion provides a reference for evaluating the voltage resistance of PCSS before withstand voltage experiments.Different insulation technique for surface protection of high-voltage are tested and different protection materials are coated on the surface of the GaAs switch.Combined with medium insulation and the surface breakdown theory

the experiment data are analyzed.The theoretical study and experiment results show that approriate insulation technique can improve the voltage resistance of GaAs PCSS efficiently

and the hold-off field strength reaches 4kV/mm.