Abstract: Relationship between the firing time and the input energy/voltage in a semiconductor bridge(SCB) was studied. A Pspice model was established by analyzing the resistor characteristics and the input energy of SCB in which BNCP dynamite was installed. Based on its errors discovered, the original model was amended so that it can be used from low energy (<5 mJ) to high energy (>40 mJ). Then the model was added into a firing circuit and simulated on different voltage and input energy conditions by the Pspice software. The conclusion drawn is that there is a minimum firing time for SCB.