Abstract: Photoconductive semiconductor switch( PCSS) has been widely investigated due to its advantages over conventional switches. Experiments show that characteristics of GaAs PCSS is closely related to various parameters such as working voltage, conduction current, triggering light, repetitive frequency, ambient environment and manufacturing procedures. Working life varies from several hundred times to a billion times under different circumstances. GaAs Photoconductive Semiconductor Switches (PCSS) with peak current over 2.42kA has been developed and tested. Degradation of GaAs PCSS is observed during working. Results show that peak conduction current is found to decrease with working shots, and dark resistance changes with working shots too .