Semiconductor device and method of manufacturing semiconductor device

The invention provides a semiconductor device and a method of manufacturing semiconductor device. Second-conductivity-type high dose impurity layers are formed in a device forming region, and function as the source and drain; a second-conductivity-type low dose impurity layer is provided around each of the second-conductivity-type high dose impurity layers so as to expand each second-conductivity-type high dose impurity layer in the depth-wise direction and in the direction of channel length, at least a part of the second-conductivity-type low dose impurity layer is positioned below the gate electrode, and the gate insulting film; and the gate insulating film has, at a portion thereof positioned above the second-conductivity-type low dose impurity layer, a sloped portion which continuously increases in the thickness from the center towards a side face of the gate electrode, without causing an inflection point.