Semiconductor device and method of manufacturing the same

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 or more second-conductivity-type, high-concentration impurity diffused layers formed in said device forming region, and function as the source and the drain of a transistor;
• second-conductivity-type, low-concentration impurity diffused layers having a concentration lower than that of said second-conductivity-type, high-concentration impurity diffused layers, formed in said device forming region, and provided respectively around said second-conductivity-type, high-concentration impurity diffused layers, so as to expand said second-conductivity-type, high-concentration impurity diffused layers in the depth-wise direction and the channel-length-wise direction;
• and
• a first-conductivity-type buried layer having a concentration higher than that of said semiconductor layer, positioned below said second-conductivity-type, low-concentration impurity diffused layer, and extended from an area below said channel forming region via an area below said device isolation film towards the outer periphery of said device isolation film.