We have investigated the relationship between interface chemistry, overlayer structure, and band bending when thin epitaxial overlayers of Ni, Al, and NiAI are grown by molecular beam epitaxy on anion-stabilized GaSexAsl−x/GaAs(001)-(2×l) surfaces. The substrates were prepared by passivating GaAs(001) with H2Se in a metal-organic chemical vapor deposition reactor. This treatment is now known to result in Se-As anion exchange in the top several anion layers, as well as a significant reduction in surface-state density. Chemistry of interface formation and band bending were monitored by x-ray photoemission. Overlayer structures were characterized by low-energy electron diffraction and x-ray photoelectron diffraction. Al, Ni, and NiAI overlayers assume fcc-R45°, metastable-bcc, and CsCl structures respectively. The free surfaces as prepared were nearly flat-band, exhibiting only ∼0.180 meV of band bending. The growth of Al, Ni, and NiAI epitaxial films at a substrate temperature of 100°C increased the band bending, resulting in Schottky barrier heights of 0.48, 0.89, and 0.90 eV, respectively. The smaller increase in band bending when Al is depositied is correlated with a lack of disruption of the anion sublattice. Ga and As 3d core-level spectra for the growth of 25 monolayers of epitaxial NiAI on GaAs(001)-c(2×8) at 100C are virtually identical to those measured for NiAI growth under the same conditions on GaSex Asl×x/GaAs(001)-(2×l). Moreover, the band bending is the same, leading to a Schottky barrier height of 0.90 eV, and establishing that the rather high Schottky barrier height at the NiAI/GaAs(001) interface is a result of Fermi-level pinning deep in the forbidden gap.