X‐ray diffraction has been used to characterize the heteroepitaxial growth of indium formed at the interfaces between ZnO thin film and InP monocrystalline substrates. The In formation was induced by a thermal degradation of InP during annealing in the range of 400–700 °C for 3 min. The results prove that the evolution of the degradation is controlled by the decomposition of close‐packed InP{111} planes, while the polar character of these planes plays a very important role. Moreover, for all four employed orientations of InP substrates [namely (111)A, (111)B, (110) and (100)], In is found to grow (101) on InP{111} planes. On an InP{111} interface plane, In crystallites can occur in six possible orientations characterized by a condition In⟨100⟩∥InP⟨110⟩. To estimate a mismatch of the heteroepitaxy, a geometrical model of the atomic arrangement at In(101)‐InP(111) interface is given. ©1996 American Institute of Physics.