The present invention relates to growth of III-V semiconductor nanowires (2) on a Si substrate (3). Controlled vertical nanowire growth is achieved by a step, to be taken prior to the growing of the nanowire, of providing group III or group V atoms to a (111) surface of the Si substrate to provide a group III or group V 5 surface termination (4). A nanostructured device comprising a plurality of aligned III-V semiconductor nanowires (2) grown on, and protruding from, a (111) surface of a Si substrate (3) in an ordered pattern in compliance with a predetermined device layout is also presented.