A semiconductor device that can suppress variation of GND potential of a control board and prevent malfunction of IC without restricting a mounting direction of the IC of the control board is provided. In a power module 10 as a semiconductor device in which an insulating board 31 having a power switching element 24 and a control board 22 having IC 50 for controlling the power switching element 24 are vertically provided in a case body 19, GND pins 61 are provided at both the sides of the IC 50, a GND pattern. 51 to which the GND pins 61 of the IC 50 are connected is provided in the control board 22, and a GND loop breaking slit 70 as a. breaking portion for breaking a GND loop formed by electrical connection of the IC 50, the GND pins 61 at both the sides of the IC 50 and the GND pattern 51 is provided to the GND pattern 51.