A memory cell includes a first insulating film hose principal constituent elements are Si, O and N, a charge storage layer whose principal constituent elements are Hf, O and N, formed on the first insulating film, a second insulating film having dielectric constant higher than that of the first insulating film and formed on the charge storage layer, and a control gate electrode formed on the second insulating film. Relation between a composition of the first insulating film and a composition of the charge storage layer is determined under the conditions that (A) a valence band offset of the first insulating film is larger than a valence band offset of the charge storage layer, and (B) a trap energy level of electrons due to oxygen vacancies in the charge storage layer exists within a bandgap of the charge storage layer.