Semiconductor device and method of forming the same

A semiconductor device comprising:

• a semiconductor substrate having a first gate groove having first and second side walls facing to each other;
• a first gate insulating film covering the first and second side walls of the first gate groove;
• a first gate electrode on the first gate insulating film, the first gate electrode being in a lower portion of the first gate groove;
• a first burying insulating film that buries the first gate groove, the first burying insulating film covering the first gate electrode;
• a first diffusion region adjacent to a first upper portion of the first gate insulating film, the first upper portion being on an upper portion of the first side wall of the first gate groove;
• and
• a second diffusion region in contact with an entire portion of the second side wall of the first gate groove.