[en] Laser activated semiconductor switches utilize instantaneous response of photoconductivity to turn on or turn off the current through the switch. It has been shown that the semiconductor switch is a good candidate for the fast opening switch applications. With a suitable choice of switch material, for which the carrier recombination time is very fast, the opening time can be as fast as subnanosecond with a very high repetition rate. The semiconductor switches can easily sustain a large voltage and conduct a high current. The authors report on the performance of high voltage operation of GaAs switches. The switches used were intrinsic GaAs and Cr: GaA of bulk devices of millimeter sizes. The range of bias voltage applied was 500 V to 2 kV. The light source was a Q-switched Nd:YAG laser with 10 ns pulse duration. The closing and opening speeds of the Cr:GaAs switches were limited by the rise time and fall time of the laser pulse. Typical off-resistances when the laser light illumination was turned off is higher than 20 MΩ, whereas the on-resistances with laser illumination can be as low as 1 Ω. Such a large ratio of off-resistance to on-resistance allowed switching efficiency of better than 99%