Arrayed Si/SiGe nanowires and their heterostructures have been formed using Au-assisted wet chemical etching combined with nanosphere lithography. Because the nanowires are formed from the as-grown films, the chemical compositions and the heterostructures along the growth direction of the formed nanowires, i.e., axial heterostructures, are replicas of that of the grown layered films. The diameter and the lateral arrangement of the nanowires are defined by the lithography method. Si and its Ge alloy nanowires and one-dimensional heterostructures formed using this method may have great potential for vertical logic, photovoltaic, and memory-device applications.