It is an object to provide a nonvolatile semiconductor memory device with an excellent writing property and charge-retention property. A semiconductor layer (14) including a channel forming region (15) between a pair of impurity regions (18) which are formed to be apart from each other is provided. In an upper layer portion thereof, a first insulating layer (16), a floating gate electrode (20), a second insulating layer (22), and a control gate electrode (24) are provided. The floating gate (20) has at least a two-layer structure, and a first layer (20a) being in contact with the first insulating layer (16) preferably has a band gap smaller than that of the semiconductor layer (14). The stability of the first layer (20a) is improved by formation of a second layer (20b) of the floating gate electrode using a metal, an alloy, or a metal compound material. Such a structure of the floating gate electrode can improve injectability of carriers in writing and a charge-retention property.
The first layer (20a) can comprise SiGe.