A method (and semiconductor device) of fabricating a TFET device provides a source region having at least a portion thereof positioned underneath a gate dielectric. In one embodiment, the TFET includes an N+ drain region and a P+ source region in a silicon substrate, where the N+ drain region is silicon and the P+ source region is silicon germanium (SiGe). The source region includes a first region of a first type (e.g., P+ SiGe) and a second region of a second type (undoped SiGe), where at least a portion of the source region is positioned below the gate dielectric. This structure decreases the tunneling barrier width and increases drive current (Id).