Semiconductor device and semiconductor device manufacturing method

A semiconductor device manufacturing method comprising the steps of:

• forming element isolation regions in a semiconductor substrate such that an element formation region is interposed between said element isolation regions and said element isolation regions are buried in said semiconductor substrate;
• forming a dummy gate on said element formation region such that said dummy gate crosses said element formation region;
• forming source-drain regions in said element formation region on both sides of said dummy gate such that junction positions of said source-drain regions are deeper than surfaces of said element isolation regions;
• forming a first insulating film on said semiconductor substrate with a surface of said dummy gate being exposed;
• forming a groove by removing said dummy gate;
• removing top parts of said element isolation regions within said groove;
• and
• forming a gate electrode on said semiconductor substrate within said groove with a gate insulating film interposed between said gate electrode and said semiconductor substrate.