A semiconductor device includes a semiconductor layer of first-conductivity-type that has a main surface and that includes an active region set at the main surface, a current detection region set at the main surface away from the active region, and a boundary region set in a region between the active region and the current detection region at the main surface, a first body region of second-conductivity-type formed in a surface layer portion of the main surface at the active region, a first trench gate structure formed in the main surface at the active region, a second body region of second-conductivity-type formed in the surface layer portion of the main surface at the current detection region, a second trench gate structure formed in the main surface at the current detection region, a well region of second-conductivity-type formed in the surface layer portion of the main surface at the boundary region, and a dummy trench gate structure formed in an electrically floating state in the main surface at the boundary region.