We have used soft x-ray photoemission spectroscopy (SXPS) to investigate the dependence of Fermi-level pinning on chemical structure at InP–metal interfaces. SXPS core level spectra of Al, Ti, Ni, Au, Pd, Ag, and Cu on UHV-cleaved InP(110) surfaces reveal evidence for semiconductor outdiffusion, metal indiffusion, metal-anion bonding and metal-cation alloying. Corresponding Fermi-level movements indicate a range of pinning positions at significantly different energies within the n-type InP band gap. These results demonstrate that the Schottky barrier heights depend sensitively on changes in interface chemical bonding and diffusion, which strongly affect the type of electrically active sites and interfacial layers formed.