We demonstrate source/drain (S/D) design for GaAs n-type metal-oxide-semiconductor field-effect transistor (NMOSFET) by embedding Ge into recessed S/D region to eliminate the intrinsic issues of the low solid solubility of dopants and low density of states (DOS) in GaAs material. For achieving high quality S/D epitaxy, the effects of substrate orientation and surface preparation on the quality of the epitaxial Ge film were investigated. High quality Ge film was successfully grown on the GaAs (111)A substrate by using a ultra high vacuum chemical vapor deposition (UHVCVD) tool and the significant improvement in the surface root-mean-square (RMS) roughness was observed as compared to that on the (100) substrate. The fabricated GaAs NMOSFET with hetero-Ge S/D exhibits an I on /I off ratio of ∼2.5 × 10 2. Even though the performance can be further improved, we think our proposed scheme sheds the light on overcoming the issues of the low solid solubility of n-dopant and low DOS in III-V MOSFETs.