We report the first demonstration of III-V n-MOSFETs with self-aligned contact technology. The self-aligned contact was formed using a salicide-like process which is compatible with CMOS process flow. A new epitaxy process was developed to selectively form a thin continuous germanium-silicon (GeSi) layer on gallium arsenide (GaAs) source and drain (S/D) regions. Nickel was deposited and annealed to form NiGeSi, and unreacted metal was removed. A second anneal diffuses Ge and Si into GaAs to form heavily n+ doped regions, and a novel self-aligned nickel germanosilicide (NiGeSi) ohmic contact was achieved. MOSFETs with the new self-aligned metallization process were realized.