The thermal desorption of thin oxide films on n‐ and p‐type InP has been studied by using x‐ray photoelectron spectroscopy. It was found that oxides formed on InP could be completely desorbed at 458 °C without causing surface decomposition. The phosphorus and indium oxides desorbed together within 5°. However, heating the oxidized surface to about 453 °C, while not changing the chemical structure of the phosphorus oxides, did remove a significant amount of indium oxides. Heating at this lower temperature also induced changes of the position of the surface Fermi level. On n‐InP, it changes from 0.1 eV below the conduction‐band minimum to 0.3 eV, and on p‐InP, from 0.6 to 0.4 eV. Upon complete desorption of all surface oxides at 458 °C, the Fermi level on n‐InP was then pinned at 0.3 eV, whereas that of p‐InP moved down to 0.9 eV. This suggests a reduction of donor defects. Heating the surface of 458 °C for more than a few minutes or heating at a slightly higher temperature caused a loss of phosphorus. On such a decomposed surface, the Fermi level of n‐InP was pinned at 0.5 eV and p‐InP at 0.7 eV, which indicates the formation of more donor and acceptor defects.