Abstract: The bus bar stray inductance is one of the key factors affecting the operational reliability of the insulated gate bipolar transistor（IGBT）. In order to obtain the influence mechanism of stray inductance on the semiconductor modules of DC circuit breakers, an optimized design method for reducing stray inductance was proposed. Firstly, the turn-off transient process of the semiconductor module of the hybrid DC circuit breaker was analyzed, and the turn-off transient equivalent circuit including stray inductance was also established. Then the influence of stray inductances on induction voltage overshoot in the IGBT turn-off process was deeply studied by means of theoretical analysis, simulation calculations and tests. The sensitivity coefficients were proposed in order to quantitatively analyze the influence of stray inductance on IGBT turn-off voltage. Furthermore, the design principles of stray inductance in diode full-bridge modules were put forward. Finally, the physical structure of the diode full-bridge module was designed and built based on the principles of sensitivity coefficient. The simulations are in good accordance with the experimental results and the accuracy of the stray inductance impact analysis has been verified. It also verifies the effectiveness of the stray inductance optimization scheme.