Nonvolatile semiconductor memory device and method of fabricating the same

A nonvolatile semiconductor memory device comprising:

• a semiconductor substrate comprising an element isolation trench;
• a tunnel insulating film on the semiconductor substrate;
• a charge storage layer on the tunnel insulating film;
• a block insulating film on the charge storage layer;
• a first element isolation insulating film in the element isolation trench, the first element isolation insulating film having a bottom surface lower in level than an interface where the semiconductor substrate and the tunnel insulating film are in contact with each other, the first element isolation insulating film having a top surface lower in level than an interface where the charge storage layer and the block insulating film are in contact with each other;
• a second element isolation insulating film on the first element isolation insulating film, the second element isolation insulating film protruding to a top surface of the block insulating film and being in contact with a side surface of the block insulating film, the second element isolation insulating film having a higher Si concentration than the block insulating film;
• and
• a control gate electrode on the block insulating film and on the second element isolation insulating film.