A method of forming a nanowire heterostructure, including, forming a dummy nanowire on a substrate, forming a sacrificial cover layer on the dummy nanowire, forming a spacer layer on a portion of the sacrificial cover layer, wherein a portion of the sacrificial cover layer extends above the top surface of the spacer layer, removing the portion of the sacrificial cover layer that extends above the top surface of the spacer layer, forming a gate structure on the spacer layer and a remaining portion of the sacrificial cover layer, forming an interlayer dielectric (ILD) layer on the gate structure, removing the dummy nanowire to form a nanowire trench, and forming a replacement nanowire in the nanowire trench.