Patent ID: 8390053

Claim:
A nonvolatile semiconductor device having a field effect transistor, the field effect transistor comprising: a gate insulating film formed on a main surface of a semiconductor substrate, the gate insulating film including a first insulating film, a charge storage layer formed over the first insulating film and having a capability to accumulate electric charges and a second insulating film formed over the charge storage layer; a gate electrode formed on the gate insulating film; a first semiconductor region formed in the semiconductor substrate under one side of the gate electrode; and a second semiconductor region formed in the semiconductor substrate such that the second semiconductor region is electrically connected to the first semiconductor region, wherein a first impurity concentration of the first semiconductor region is lower than a second impurity concentration of the second semiconductor region, the gate insulating film has a first portion which overlaps the first semiconductor region and a second portion which does not overlap the first semiconductor region, the first portion and the second portion located next to each other in a gate length direction, the first portion has a third portion and a fourth portion located next to each other in the gate length direction, the third portion includes the first insulating film, the charge storage layer and the second insulating film, the fourth portion includes the first insulting film and the second insulating film, the charge storage layer is not included in the fourth portion, the fourth portion is disposed adjacent an edge of the gate electrode, and the gate insulating film does not overlap the second semiconductor region.