A multiple-bit transistor includes P type semiconductor including a projection, a gate insulation layer, a pair of N type source/drain regions, tunnel insulation layers, a pair of floating gates, inter-polycrystalline insulation layers, and a control gate. The root portion of the projection, which is defined by a straight line virtually connecting the source/drain regions, is higher in the concentration of the P type impurity than the other portion. A potential difference for write-in is set up between the source/drain regions while a write voltage is applied to the control gate, thereby causing electrons to be ballistically injected into at least one of the floating gates.