A semiconductor device and a fabricating method thereof are provided. The semiconductor device includes a substrate, a first nanowire spaced apart from a first region of the substrate, a first gate electrode surrounding a periphery of the first nanowire, a second nanowire spaced apart from a second region of the substrate and extending in a first direction and having a first width in a second direction intersecting the first direction, a supporting pattern contacting the second nanowire and positioned under the second nanowire, and a second gate electrode extending in the second direction and surrounding the second nanowire and the supporting pattern.