The development of a picosecond GaAs photoconduotive switch is reported. The switch consists of a miorostrip transmission line formed on Cr-doped semi-insulating GaAs with a small gap (-20μm) in the stripline. As the source of optical pulses used for preliminary evaluation of the switch, a synchronously pumped Rh6G dye laser was used. The rise time of the signal observed on a sampling oscilloscope was 120 ps and the FWHM was 230ps. We measured the dependence of peak voltage of the switched electric pulse on the energy of the incident laser pulse for a bias voltage of 30 V and incident energy range of 38~220 pJ.