The growth of high-quality stoichiometric indium phosphide by atmospheric pressure metal–organic chemical vapor deposition within thin-film artificial opals has been optimized. The optical properties of these systems have been studied as a function of the filling fraction. A consistent behavior has been found which substantially differs from that of other common infilled opals. The evolution of the InP morphology seems to be strongly correlated with this anomalous photonic response. At the first infiltration stages, the growth leads to the formation of nanocrystallites that eventually, as the infiltration increases, coalesce in single-crystalline grains of increasing size. The possibility to oxidize the material adds to its potential as a useful optical material.