In this paper, variant III of the CuAu-I-type ordering of AlxGa1−xAs on (110), (111)A and (001) GaAs substrates is determined for different growth temperatures and Al fractions. For this purpose AlxGa1−xAs films were produced by metal organic chemical vapour deposition and analysed 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-I-type structure, followed by the disordered phase. Generally, a higher ordering is observed for high growth temperatures and for samples with an Al fraction of 50%. Furthermore, 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 close to the ordering degree 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-I-type ordering is observed for the first time.The lowest detection limit is estimated to be S=0.0009±0.0006, which makes it possible to measure CuAu-I-type reflections of alternating Al0.5005Ga0.4995As and Al0.4995Ga0.5005As monolayers. For the highest ordered sample, (110) Al0.50Ga0.50As grown at 750°C with S=0.053±0.014, the alloy consists of alternating Al0.527Ga0.473As and Al0.473Ga0.527As monolayers along the [001] direction.