In order to reduce electric field concentration in a semiconductor device including a main transistor section and a sense transistor section, the semiconductor device is provided, the semiconductor device including a semiconductor substrate of a first conductivity type, a main transistor section in an active region on the semiconductor substrate, and a sense transistor section outside the active region on the semiconductor substrate, wherein the active region is provided with a main well region of a second conductivity type, and wherein the sense transistor section has a sense gate trench section formed extending from the outside of the active region to the main well region on the front surface of the semiconductor substrate.