A method of manufacturing a semiconductor device includes forming a first semiconductor layer having a first composition over a semiconductor substrate, and forming a second semiconductor layer having a second composition over the first semiconductor layer. Another first semiconductor layer having the first composition is formed over the second semiconductor layer. A third semiconductor layer having a third composition is formed over the another first semiconductor layer. The first semiconductor layers, second semiconductor layer, and third semiconductor layer are patterned to form a fin structure. A portion of the third semiconductor layer is removed thereby forming a nanowire comprising the second semiconductor layer, and a conductive material is formed surrounding the nanowire. The first semiconductor layers, second semiconductor layer, and third semiconductor layer include different materials.