Vertical MOSFET and method of manufacturing the same

A vertical metal oxide semiconductor field effect transistor, comprising:

• a trench formed in a major surface of a semiconductor substrate, said trench having a botom and side walls substantially normal to said major surface;
• a first insulating film overlying at least one of said side walls and a portion of said major surface;
• a first conductive layer formed on a portion of said first insulating film and overlying said at least one of said side walls and at least part of said portion of said major surface, said first conductive layer serving as a gate electrode;
• a second insulating film formed on said first conductive layer;
• lower and upper diffusion layers formed in said bottom of said trench and in a surface layer of said semiconductor substrate, said diffusion layers serving as source/drain regions, respectively;
• and
• a second conductive layer formed in contact with said lower diffusion layer in said bottom of said trench, said second conductive layer being insulated from said first conductive layer by said second insulating film and serving as the electrode for said lower diffusion layer.