There is an unintended inductance called stray inductance in the power module. For modules with a switching function, the inductance should be reduced to make power loss during overshoot smaller. In this experiment, design variables were defined as the structure of the module, and the inductance was calculated from design variables. The design optimization was performed by the response surface methodology. As a result of calculating the performance for the optimized structure, the inductance was confirmed to be reduced by 12.1% from the original structure. The contribution distribution of each design variable to the inductance was also obtained.