Semiconductor device and method of manufacturing semiconductor device

A semiconductor device comprising:

• a device isolation film formed in a first-conductivity-type semiconductor layer;
• a device forming region partitioned by said device isolation film;
• a channel-forming region provided to said device forming region;
• a gate insulating film positioned over said channel-forming region;
• a gate electrode positioned over said gate insulating film;
• at least two second-conductivity-type high dose impurity layers formed in said device forming region, and function as the source and drain of a transistor;
• and
• a second-conductivity-type low dose impurity layer formed in said device forming region, provided respectively around each of said second-conductivity-type high dose impurity layers so as to expand said second-conductivity-type high dose impurity layers in the depth-wise direction and in the direction of channel length, and has an impurity concentration lower than that of said second-conductivity-type high dose impurity layer,
• at least a part of said second-conductivity-type low dose impurity layer being positioned below said gate electrode, and
• said gate insulating film having, at a portion thereof positioned above said second-conductivity-type low dose impurity layer, a sloped portion which continuously increases in the thickness from the center towards a side face of said gate electrode, without causing an inflection point.