In the present paper variant III of the CuAu-I-type ordering of AlxGa1-xAs on (110), (111)A and (001) GaAs substrates is determined for different temperatures and Al fractions. For this purpose AlxGa1-xAs films were produced by metal organic chemical vapor deposition and analyzed using X-ray diffraction at the European Synchrotron Radiation Facility in Grenoble. It is found that the ground state of AlxGa1-xAs is given by the CuAu-1-type structure, followed by the disordered phase. Generally, a higher degree of order is observed for high growth temperatures and for samples with an Al fraction of 50%. With respect to the substrate orientation the ordering is found to be strongest for samples grown on (110) substrates with a maximum long-range order parameter S of 0.053 +/- 0.014, followed by the samples grown on (111)A and (001) substrates with an S of 0.011 +/- 0.005 and 0.0025 +/-0.0017, respectively. Because of symmetrical considerations, a total S of 0.033 +/- 0.015 is expected for the (111)A samples. This is more than half the ordering of the (110) samples, reflecting the (110)-like surface configuration of the (111)A face at higher temperatures. For the (001) samples the variant III CuAu-1-type ordering is observed for the first time. (c) 2005 Elsevier B.V. All rights reserved.