Recently several groups (see for example Refs. 1-9) have been investigating optically initiated GaAs avalanche switches first introduced by Williamson et al. (10). Although the configurations vary, these switches have the following common properties: a gain on the order of 1000 in current over that expected from the injected photocarriers, switching at fields several times lower than the published GaAs avalanche field, a very fast rise time typically occurring a few nanoseconds after the start of the laser pulse, and the device eventually evolving into a lock-on condition characterized by a fixed voltage drop proportional to the electrode spacing. At this time a complete understanding of the device physics is lacking. Theoretical investigation of field enhancement from the injected carriers has shown that this effect is not large enough to produce the initial avalanche (8). Both Gunn (3-5,7,9) and impurity (2,3,6) effects have been suggested as important aspects of the device operation during the lock-on condition. In the next two sections, we describe an empirical model of the initial switching of the device followed by comparing the model predictions to data obtained on doughnut hole configuration devices. The last section discusses the implications of the model on the device physics.