A current-controlled model of semiconductor opening switch(SOS) was developed to study the current opening effect and the physical process of SOS in pulsed power system. The p+-p-n-n+ type SOS was analyzed on the basis of the model. The distributions of carriers and field in SOS were simulated during forward and reverse current pumping, and the current opening effect was obtained. The results show that the opening process starts first at the p-type region.