The mechanism of growth of GaP on a cleaved CaF2(111) surface was studiedin situin a high‐energy reflection electron diffraction system. It was found that in the early stages of growth, GaP forms tetrahedral nuclei with {111} faces. The three edges of the tetrahedron are parallel to the three ⟨110⟩ directions. These microcrystals coalesce and form a smooth film after a mean thickness of more than 300 monolayers of GaP is deposited on the surface. Temperatures for epitaxial growth of a single crystal without twinning as a function of the atom arrival rate were studied for GaP on a clean CaF2surface and on a GaP‐covered CaF2surface. It was found that growing GaP without twinning on a bare cleaved CaF2surface requires a temperature ∼65°C higher than on a surface that is covered with GaP. The structural characteristics of the GaP film as a function of the substrate temperature are also discussed.