A semiconductor device includes: a substrate doped with a first conductive type; a first nanowire protruding on the substrate in a first direction and including a first core and a first shell; and an electrode being on the first nanowire and directly contacting a top surface of the first core, wherein the first shell covers a sidewall of the first core; the first shell includes a first semiconductor; and the first core includes a second semiconductor having a different bandgap than the first semiconductor.