We report the demonstration of an n-channel lateral Si tunnel field-effect transistor (TFET) with a single crystalline Ge source fabricated using the gate-last process.The p+ Ge source was in situ doped and grown at 320°C.An abrupt interface between Ge source and Si channel with type-lⅡ band alignment and a steep source doping profile (～1.5nm/decade) formed the tunneling junction.This alows the realization of a TFET with a steep subthreshold swing of 49mY/decade at room temperature and an ION/IOFF ratio of 107.