The growth of AlxGa1−xP for Al mole fractions between 0 and 1 has been achieved on (100) GaP substrates using gas source molecular beam epitaxy with elemental Ga and Al, and P2cracked from PH3as the source materials. The observed reflection high energy electron diffraction pattern of the GaP surface indicates that an exponential increase in the incident P2flux is required to maintain good morphology beyond 690 °C. This temperature was found to correspond closely to the congruent vaporization temperature of Ga from the growth surface. The addition of Al on the surface was found to substantially increase the Ga congruent vaporization temperature from the GaP surface. The growth rates for AlxGa1−xP as a function of growth temperature between 600 and 750 °C were determined by transmission electron microscopy. Using elemental Si as ann‐type dopant, free electron concentrations as high as 1.65×1019cm−3in GaP and 1.5×1019cm−3in Al0.28Ga0.72P were achieved.