The influence of thermal annealing on Sb/GaAs(110) interfaces is studied in situ by high-resolution photoemission spectroscopy. A detailed line-shape analysis of the Sb 4d core-level spectra shows that Sb deposition at room temperature (RT) does not lead to perfectly ordered growth of the first monolayer (ML), as was assumed so far. Annealing at 330°C results in a highly ordered overlayer that is desorption limited to 1 ML. The degree of order affects the barrier height at the interface drastically: While RT deposition pins the Fermi level 0.6 eV above valence-band maximum for p-type GaAs, we find a reduction in the band bending by a factor of 2 after annealing. © 1987 The American Physical Society.