The formation of discrete phase GaP by diffusion of phosphorus into GaAs at pressures of 10 to 30 atm and temperatures of 800° to 900°C is described. X‐ray data identifying GaP are given. A mechanism is postulated for the step‐like concentration gradients observed. Striae supporting this hypothesis were observed and are illustrated. Epitaxial growth as a factor is considered but not believed a significant factor based on microscopy and experimental environment.