Semiconductor device with groove type channel structure

A semiconductor device comprising:

• a semiconductor substrate;
• a gate insulator film formed on a bottom surface and a side surface of a groove formed in said semiconductor substrate;
• a gate electrode having a lower portion buried in said groove on whose bottom surface and side surface said gate insulator film is formed, and an upper portion protruding from a surface of said semiconductor substrate;
• and
• a source region and a drain region formed on a surface region of said semiconductor substrate in such a way as to sandwich said gate electrode,
• wherein said semiconductor device satisfies an equation
• L+Xj−tOX<H<3.125×Lgate+Xj−tOX
• where L is a channel length of a channel region formed along said groove, tOX a thickness of said gate insulator film, H is a thickness of said gate electrode, Lgate is a length of said gate electrode, and Xj is the junction depth of a source/drain diffusion region.