A semiconductor layer having a channel formation region provided between a pair of impurity regions spaced from each other is provided, and a first insulating layer a floating gate, a second insulating layer, and a control gate are provided above the semiconductor layer. The semiconductor material forming the floating gate preferably has a band gap smaller than that of the semiconductor layer. The band gap of a channel formation region in the semiconductor material forming the floating gate is preferably smaller than that of the semiconductor layer by 0.1 eV or more.