A theoretical model has been developed that describes operation of a high-power semiconductor current interrupter (SOS diode) with allowance for the space charge formation. According to this model, as well as to the models based on the quasineutral approximation, the process of current breakage in a semiconductor structure of the SOS diode is related to the formation of strong field regions in highly doped parts of the structure. The space charge decreases the role of avalanche multiplication, thus providing for higher switching characteristics of the diode.