The thermal decomposition of a gallium tribromide‐ammonia complex in an ammonia, argon, or nitrogen atmosphere has been used for the deposition of gallium nitride films on silicon and hexagonal silicon carbide substrates in a gas flow system. The substrate temperature and the nature of the ambient are the most important parameters of the deposition process. Adherent and transparent films of gallium nitride have been deposited at substrate temperatures up to about 600°C in an ammonia atmosphere and up to about 750°C in a nitrogen or argon ambient. At higher temperatures, the deposit became contaminated with gallium. The gallium nitride films deposited on {111} oriented silicon substrates at 600°–700°C were found to show a (110) fiber orientation. Epitaxial, single crystalline gallium nitride films have been grown successfully on the basal plane of hexagonal silicon carbide substrates at 520°–600°C. These films are of high resistivity indicating that the thermal decomposition of gallium nitride is negligible. Thus, the thermal decomposition of the gallium tribromide‐ammonia complex provides a new promising technique for the crystal growth of gallium nitride.