Epitaxial layers of alloys are grown on sapphire (0001) and silicon (111) substrates by MOVPE in an ambient gas at atmospheric pressure. By optimizing the reactor design and the growth conditions, parasitic reactions of metalorganic compounds with gaseous are remarkably reduced and the composition of layers can be controlled fairly well for the first time. The vapor‐solid distribution coefficient for Al is found to be approximately unity. At respective substrate temperatures of 1020°C for sapphire and 1050°C for silicon, single‐crystal layers of withx up to 0.40 are obtained. The lattice constant is proportional to the molar fraction of following Vegard's law. The electrical resistivity, carrier concentration, and Hall mobility of the layers are studied as a function of the composition.