A method for fabricating a semiconductor nanowire device includes forming a base including a plurality of PMOS regions, forming a plurality of first openings in the base of the PMOS regions, forming a plurality of first epitaxial wires by filling the first openings with a germanium-containing material, and forming a plurality of second openings in the base by etching a portion of the base under each first epitaxial wire. Each first epitaxial wire is connected to both sidewalls of a corresponding second opening and is hung above a bottom surface of the corresponding second opening. The method also includes performing a thermal oxidation treatment process on the plurality of first epitaxial wires to form an oxide layer on each first epitaxial wire, forming a plurality of first nanowires by removing the oxide layer from each first epitaxial wire, and forming a first wrap-gate structure to surround each first nanowire.