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 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 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 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 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 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 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 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 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 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. <EOS>