The reverse‐biased performance of a molecular‐beam‐epitaxy‐grown high‐power optothyristor has been systematically characterized for pulsed power‐switching applications. The device has aP+N‐SI‐PN+thyristor‐like structure with the bipolar junctions formed by AlGaAs. The semi‐insulating (SI) GaAs used is liquid‐encapsulated‐Czochralski grown, undoped, and 650 &mgr;m in thickness. It is found that the reverse‐biased optothyristor can be triggered by a light‐emitting diode operated at 10−5W, and miniature semiconductor lasers can trigger the switch with 132 A current using only a 1‐mm‐diam optical aperture. The reverse switchingdi/dtand the maximum peak current are reported as a function of blocking voltage. The effects of bipolar junctions on both sides of the SI‐GaAs are also reported by comparing the bulk photoconductive current with the optothyristor switched current. It is shown that a laser beam of 0.05 &mgr;J can be used to trigger on and switch about the same current as a 0.3 &mgr;J laser beam, suggesting the possibility of integrating miniature semiconductor lasers and the optothyristors on the same chip to form a portable, compact, high‐power solid‐state pulser.