UV photochemical deposition of Sn films on GaAs (001) surfaces from a variety of tin‐containing compounds (tetramethyltin, tetrabutyltin, dibutyltin dibromide, stannic chloride, hexamethylditin, dibutyltin sulfide, and iodotrimethyltin) was studied. X‐ray photoelectron spectroscopy showed that during the initial stages of deposition from the halogenated compounds, the GaAs surface was photochemically etched, most likely by a halogen radical species. The photochemical etching resulted in an arsenic deficient surface which was particularly dramatic for the case of SnCl4. These results have important implications for the choice of sources for photochemical deposition when the metal‐semiconductor interface is important and for photochemical etching if stoichiometric surfaces are required.