Semiconductor device and method of manufacturing the same

A method of manufacturing a semiconductor device comprising:

• forming a high impurity concentration layer of a first conductivity type in at least a part of a semiconductor substrate of the first conductivity type;
• forming an epitaxial Si layer of the first conductivity type in contact with said high impurity concentration layer by an epitaxial growth method on a main surface of the semiconductor substrate;
• selectively removing the epitaxial Si layer and the semiconductor substrate to form a trench, followed by burying an insulating film for element isolation in said trench;
• and
• forming a source region and a drain region in a region where the insulating film for element isolation is not formed, the epitaxial Si layer being interposed between the source region and the drain region,
• wherein said source region includes a first source region whose undersurface is at a low position and a second source region whose undersurface is at a position higher than the undersurface of the first source region,
• said drain region includes a first drain region whose undersurface is at a low position and a second drain region whose undersurface is at a position higher than the undersurface of the first drain region, and
• a level of the undersurfaces of the first source region and the first drain region is lower than a level of an interface between an undersurface of said epitaxial Si layer and a surface of said high impurity concentration layer.