Submonolayer to several monolayers of In were evaporated onto the GaP(1̄ 1̄ 1̄) (1×1) clean surface at room temperature to investigate the formation of In/GaP(1̄ 1̄ 1̄) interface. From the electron energy loss spectra, it has been shown that the surface electronic states related with the Ga dangling bonds are significantly affected by the deposited In atoms even at initial stage. The growth mode of In overlayers on GaP(1̄ 1̄ 1̄) is island like rather than layer‐by‐layer form. By increasing the amount of deposited In atoms, the In islands become larger and thicker, as evaluated from the relative peak intensities of the bulk and plasmon losses. The core‐level photoelectron specrtra show there is no indication of the occurrence of In–Ga interfacial exchange reaction. The valence band ultraviolet photoelecton spectroscopy reveals a new peak structure at the energy of 5.2 eV below Fermi level, which is believed to be attributed by metallic In. In the case of Ga on InP, it has already been verified that the Ga–In interchange reaction does exist and is quite remarkable. It does not seem sufficient to explain the irreversibility of surface interchange reaction between Ga/InP and In/GaP simply by means of thermodynamical consideration. The surface migration coefficient and the stability of metallic clusters may play a complementary role in determining the surface chemical reactivity.