Disclosed is a semiconductor device (e.g., nonvolatile semiconductor memory device) and method of forming the device. The device includes a gate electrode (e.g., floating gate electrode) having a first layer of an amorphous silicon film, or a polycrystalline silicon thin film or a film of a combination of amorphous and polycrystalline silicon, on the gate insulating film. Where the film includes polycrystalline silicon, the thickness of the film is less than 10 nm. A thicker polycrystalline silicon film can be provided on or overlying the first layer. The memory device can increase the write/erase current significantly without increasing the low electric field leakage current after application of stresses, which in turn reduces write/erase time substantially. In forming the semiconductor device, a thin amorphous or polycrystalline silicon film can be provided on the gate insulating film, and a thin insulating film provided on the amorphous silicon film, with a thicker polycrystalline silicon film provided on or overlying the thin insulating film. Where the thin silicon film is amorphous silicon, it can then be polycrystallized, although it need not be. Also disclosed is a technique for selective crystallization of amorphous silicon layers, based upon layer thickness.