This invention discloses a method of synthesizing a Group III-V compound semi-conducting film from a Group III metal alkyl and Group V hydride wherein the method comprises providing a vacuum chamber in which the synthesis takes place, adsorbing at least one monolayer of said Group III metal alkyl on an inert surface, backfilling the chamber with a Group V hydride, adsorbing the Group V hydride on the inert surface, providing atomic hydrogen atoms from electron-induced dissociation of Group V hydride adsorbed on the surface, inducing an electron-induced depletion of carbon at a rate which is dependent on the pressure of the Groups V hydride, retaining substantially all Group III metal on the surface and providing a thermally stable Group III-V compound semi-conducting film on the inert SiO.sub.2 surface. Methods for synthesizing a multilayer Group III-V semi-conducting film and specifically a GaN film are also disclosed, along with the apparatus for the synthesis of Group III-V compound semi-conducting films.