Abstract: As the key components of all solid-state pulse sources, semiconductor opening switches have the advantages of high frequency, long life, fast interruption, and large power capacity. The pre-pulse in output pulse voltage of semiconductor opening switches seriously affects the pulse rise time and the repetition frequency of the system. In this paper, the mechanism of the pre-pulse during the reverse interruption process is studied. The evolution process of the carriers and the electric field during the forward and reverse pumping processes of the semiconductor opening switches are investigated by using the simulation software Silvaco-Atlas. It is found that the pre-pulse is caused by the N-N⁺ junction interruption in the bilateral interruption process. The length of pre-pulse depends mainly on the mobility of minorities in the P-type region, and the slope of the pulse depends on the PN interruption process. Meanwhile, the devices with different base region lengths and different pumping conditions have been simulated and compared. It is found that the device base region is narrower, the pulse rises faster, and the pre-pulse is almost equal with each other. Under low current density conditions, only N-N⁺ junction interruption occurs; under high current density, bilateral interruption occurs. The delay of bilateral interruption is longer, but the pulse rises faster.