A semiconductor device including a substrate having an active region is disclosed. A field-plate region and a bulk region are in the active region, wherein the bulk region is at a first side of the field-plate region. At least one trench-gate structure is disposed in the substrate corresponding to the bulk region. At least one source-doped region is in the substrate corresponding to the bulk region, wherein the source-doped region surrounds the trench-gate structure. A drain-doped region is in the substrate at a second side opposite to the first side of the field-plate region, wherein an extending direction of length of the trench-gate structure is perpendicular to that of the drain-doped region as viewed from a top view perspective.