A heterojunction-based optothyristor has been fabricated and tested with biasing held intensity up to 34 kV/cm for pulsed power applications. It is observed that the reverse-biased optothyristor can even be triggered by a light-emitting diode (LED) of a few microwatts power and more than 500 times reduction in the required LED power for triggering has been observed when compared to bulk photoconductive switches. The optothyristor, however, does not turn on under similar triggering conditions if bias polarity is changed. The sensitive optical gating of the reverse-biased optothyristor is due to i) the wider bandgap AlGaAs optical window action, ii) the doped n and p layers that act as electron and hole guns which emit carriers into the SI-GaAs, and iii) the reverse-biased n+-p and p+-n junctions which provide large tunneling current and help in collecting photo-generated electrons and holes, respectively. The turnon delay time under reverse bias has also been studied as a function of the LED power (Pop) and is found to depend inversely proportional to the square root of Pop. The possibility of improving the switching efficiency by superimposing semiconductor laser pulse on a constant lower level background illumination has also been demonstrated.