X‐ray photoemission spectroscopy data are used to correlate the interface Fermi‐level pinning energyEiFand the corresponding interface chemistry forn‐type andp‐type InP (100) samples simultaneously subjected to a series of surface treatments. Interfaces of Schottky‐barrier contacts formed during a sequence of Au and of Al depositions made both onto chemically etched and thermally cleaned InP surfaces were investigated. Changes inEiFof up to ∼0.6 eV in the upper half of the InP band gap occurred in response to changes in interface chemistry. The observed behavior ofEiFis interpreted in terms of a single defect model with multiple charge states.