Semiconductor device and method of manufacturing the same

PROBLEM TO BE SOLVED: To provide a semiconductor device improving driving capabilities.SOLUTION: A semiconductor device comprises: a trench part 3 formed thereon for providing a concave part which changes its depth intermittently in a gate width direction; a gate electrode 7 formed inside and on an upper surface of the trench part 3 through a gate insulator film 6; a source region 9 formed at one side of the gate electrode 7 in a gate length direction; and a drain region 10 provided at the other side. Ion implantation is performed by adding impurity through inner wall of the trench 3 before the gate electrode 7 formed, and then heating treatment is performed for diffusion and activation, so that the trench part 3 can be formed with depth from a top face to a bottom part at least one part of the source region 9 and the drain region 10. Current carried with concentration on a top face of the concave part of the gate electrode 7 is then carried in the whole trench part 3 evenly, and the concave part whose depth is variable in the gate width direction has its gate effective width expanded. In the semiconductor device, on-resistance is decreased and driving performance is increased.