Abstract: A method of fabricating a compositional semiconductor device comprising a antum well wire or quantum dot superlattice structure, in particular a device selected from the group comprising lasers, photodiodes, resonant tunneling transistors, resonant tunneling diodes, far infrared detectors, far infrared emitters, high electron mobility transistors, solar cells, optical modulators, optically bistable devices and bipolar transistors, by epitaxial growth of the superlattice structure on a semiconductor substrate, is characterised in that the epitaxial growth is effected on a {311}, {211}, {111} or {110} substrate, and that the devices preferably have length and width dimensions less than 500 .ANG. and especially less than 300 .ANG..