According to one embodiment, a semiconductor device including: a substrate; a gate electrode formed above the substrate; a gate insulating film formed under the gate electrode; a channel layer formed under the gate insulating film by using a channel layer material; a source region and a drain region formed in the substrate so as to interpose the channel layer therebetween in a channel direction; and a source extension layer formed in the substrate between the channel layer and the source region so as to overlap a source-side end portion of the channel layer. The source extension layer forms a heterointerface with the channel layer. The heterointerface is a tunnel channel for carries.