The first observation of atomic long range ordering inAlxGa1−xNthin films grown by electron cyclotron resonance assisted molecular beam epitaxy on sapphire and 6H-SiC substrates is reported. The phenomenon was investigated by studying the superlattice peaks (0001), (0003), and (0005) using x-ray diffraction. The relative intensity of these peaks was found to be largest for Al content in the 30&percent;–50&percent; range in qualitative agreement with expectations for an ordered structure of idealAl0.5Ga0.5Nstoichiometry. The average size of the ordered domains in the films was found to be within a factor of 4 of the films’ thicknesses. The degree of ordering depends on the III/V flux ratio and exhibits a weaker dependence on Si doping. ©1997 American Institute of Physics.