Selective epitaxy is the laterally controlled growth of epitaxial material on a substrate. We have demonstrated the highly selective epitaxial growth of GaAs using diethyl gallium chloride or (C2H5)2GaCl. No GaAs growth is observed on the masking material over a wide range of growth temperatures, 600 ≤T ≤800°C. The edges of the selectively grown GaAs are bounded by the slow growth planes typical of the inorganic based growth techniques. By appropriate pre-growth treatment the electrical properties of the interface between the selectively grown material and the underlying substrate can be made to be very good with no interfacial potential barrier. © 1990.