Semiconductor device

A semiconductor device comprising:

• a semiconductor substrate having a first area and a second area;
• a first field effect transistor disposed in the first area, said first field effect transistor including a first gate electrode formed on the semiconductor substrate with a first gate insulation film therebetween, a pair of first impurity diffused areas formed in areas sandwiching the first gate electrode, and a pair of first sidewall portions disposed adjacent to the first gate electrode, said first sidewall portions including a first lower insulation film and a first charge accumulation film laminated sequentially, said first lower insulation film containing at least one of a silicon thermal oxide film and a non-doped silicate glass;
• and
• a second field effect transistor disposed in the second area, said second field effect transistor including a second gate electrode formed on the semiconductor substrate with a second gate insulation film therebetween, a pair of second impurity diffused areas formed in areas sandwiching the second gate electrode, and a pair of second sidewall portions disposed adjacent to the second gate electrode, said second sidewall portions having a width along a gate longitudinal direction larger than that of the first sidewall portions, said second sidewall portions including a second lower insulation film and a second charge accumulation film laminated sequentially, said second lower insulation film containing a non-doped silicate glass, said second lower insulation film having a thickness larger than that of the first lower insulation film.