SOI semiconductor device with insulating film having different properties relative to the buried insulating film

A semiconductor device comprising:

• an element-forming layer formed on a buried insulating film of a semiconductor substrate;
• a gate insulating film formed on the element-forming layer;
• a gate electrode formed on the gate insulating film;
• a source region and a drain region formed in the element-forming layer, corresponding to two sides of the gate electrode, respectively, and lying at a level higher than a surface of the element-forming layer;
• and
• an insulating film distinct from the buried insulating film and formed on a first part of the buried insulating film, which lies below the source and drain regions, said insulating film contacting bottom surfaces of the source and drain regions,
• wherein the element-forming layer has a first part and a second part, the first part of the element-forming layer corresponds to the source and drain regions, the second part of the element-forming layer is located below the gate electrode and is thicker than the first part, and the source and drain regions have bottom surfaces that contact the insulating film.