Single crystal AlP layers up to 0.1 cm thick and 2 cm in diameter have been grown onto silicon and GaAs substrates by using an open‐tube vaportransport technique. Iodine was found to be more satisfactory than chlorine for transporting aluminum at moderately low temperatures (source at 1100°C; substrate at 900°C). It was essential that the phosphorus vapor be introduced downstream from the aluminum source to prevent the formation of AlP at the source and the eventual retardation of the transport process. The asgrown layers are invariably n‐type containing greater than . Characteristics of n‐p, AlP‐Si heterojunctions were obtained and are discussed.