Detailed analysis of x‐ray rocking curves was used to determine the depth profile of strain and composition in a 2500‐A˚‐thick layer of AlxGa1−xAs grown by metalorganic chemical vapor deposition on ⟨100⟩ GaAs. Thexvalue and layer thickness were in good agreement with the values expected from growth parameters. The presence of a transition region, 280 A˚ thick, was detected by the rocking curve. In this region, the Al concentration varies smoothly from 0 to 0.87. Measurement and control of the sharpness of such interfaces has important implications for heterojunction devices.