Semiconductor (e.g. silicon, germanium) nanowires have gained interest as an attractive platform to fabricate field effect transistors devices because of their reduced short channel effects by comparison to planar devices . The realization of high performance nanowire devices however has been stymied primarily by large source (S) and drain (D) contact resistances. Here we report the fabrication and electrical characterization of the top-gated Ge-Si xGe1-x core-shell nanowire field-effect transistors (NWFETs) with highly doped S/D. The highly doped S/D, realized using low energy ion implantation, allows an efficient carrier injection into the NWFET channel.