Persistent photoconductivity in copper‐compensated, silicon‐doped semi‐insulating gallium arsenide with a time constant as large as 30 &mgr;s has been excited by sub‐band‐gap laser radiation of photon energy greater than 1 eV. This photoconductivity has been quenched on a nanosecond time scale by laser radiation of photon energy less than 1 eV. The proven ability to turn the switch conductance on and off on command, and to scale the switch to high power could make this semiconductor material the basis of an optically controlled pulsed‐power closing and opening switch.