A MONOS type non-volatile semiconductor memory device which is capable of electrically writing, erasing, reading and retaining data, the memory device including source/drain regions, a first gate insulating layer, a first charge trapping layer formed on the first gate insulating layer, a second gate insulating layer formed on the first charge trapping layer, and a controlling electrode formed on the second gate insulating layer. The first charge trapping layer includes an insulating film containing Al and O as major elements and having a defect pair formed of a complex of an interstitial O atom and a tetravalent cationic atom substituting for an Al atom, the insulating film also having electron unoccupied levels within the range of 2 eV-6 eV as measured from the valence band maximum of Al2O3.