A nonvolatile semiconductor memory device includes a first dielectric layer formed on the major surface of a semiconductor substrate, a floating gate electrode layer formed on the first dielectric layer, a second dielectric layer obtained by sequentially forming, on the floating gate electrode layer, a lower dielectric film mainly containing silicon and nitrogen, an intermediate dielectric film, and an upper dielectric film mainly containing silicon and nitrogen, a control gate electrode layer formed on the second dielectric layer, and a buried dielectric layer formed by covering the two side surfaces in the gate width direction of the stacked structure including the above-mentioned layers. The nonvolatile semiconductor memory device further includes a silicon oxide film formed near the buried dielectric layer in the interface between the floating gate electrode layer and lower dielectric film.