An As-stabilized Al0.7Ga0.3As(100) surface grown by molecular-beam epitaxy was studied using photoemission techniques. Core-level shifts and relative emission intensities at the surface were used to deduce the surface structure. High-energy-electron-diffraction and surface-contamination-rate measurements were also made. The results indicate that this surface is very similar to the As-stabilized GaAs(100)-c (2×8) surface in structure with complete depletion of Al at the surface. © 1982 The American Physical Society.