A semiconductor device comprising: a semiconductor substrate including a trench provided in an upper surface of the semiconductor substrate; a gate insulating film covering an inner surface of the trench; and a gate electrode arranged in the trench; wherein the semiconductor substrate comprises a first conductivity type first region being in contact with the gate insulating film covering both side surfaces (31, 32) of the trench; a second conductivity type second region provided below the first region and being in contact with the gate insulating film covering both side surfaces (31, 32) of the trench; and a first conductivity type third region provided below the second region and being in contact with the gate insulating film covering both side surfaces (31, 32) and a bottom surface of the trench, the bottom surface of the trench is provided so that a center part of the bottom surface protrudes upward with respect to a peripheral part of the bottom surface in a direction along which the first side and the second side of the trench face each other, and a thickness of the gate insulating film covering the peripheral part is thicker than a thickness of the gate insulating film covering the center part, characterized in that the bottom surface of the trench comprises a first slant surface extending from the center part to one side surface of the trench and a second slant surface extending from the center part to another side surface of the trench, and an angle formed by the first slant surface and the second slant surface is not more than 90 degrees. a semiconductor substrate including a trench provided in an upper surface of the semiconductor substrate; a gate insulating film covering an inner surface of the trench; and a gate electrode arranged in the trench; wherein the semiconductor substrate comprises a first conductivity type first region being in contact with the gate insulating film covering both side surfaces (31, 32) of the trench; a second conductivity type second region provided below the first region and being in contact with the gate insulating film covering both side surfaces (31, 32) of the trench; and a first conductivity type third region provided below the second region and being in contact with the gate insulating film covering both side surfaces (31, 32) and a bottom surface of the trench, a first conductivity type first region being in contact with the gate insulating film covering both side surfaces (31, 32) of the trench; a second conductivity type second region provided below the first region and being in contact with the gate insulating film covering both side surfaces (31, 32) of the trench; and a first conductivity type third region provided below the second region and being in contact with the gate insulating film covering both side surfaces (31, 32) and a bottom surface of the trench, the bottom surface of the trench is provided so that a center part of the bottom surface protrudes upward with respect to a peripheral part of the bottom surface in a direction along which the first side and the second side of the trench face each other, and a thickness of the gate insulating film covering the peripheral part is thicker than a thickness of the gate insulating film covering the center part, characterized in that the bottom surface of the trench comprises a first slant surface extending from the center part to one side surface of the trench and a second slant surface extending from the center part to another side surface of the trench, and an angle formed by the first slant surface and the second slant surface is not more than 90 degrees.