The doping of molecular beam epitaxial GaAs with erbium up to a concentration of 2×1019cm−3has been successfully demonstrated. Up to a concentration of about 5×1018cm−3the surface morphology remained good but for higher doping levels the surface became structured. Hall and profile measurements indicate that erbium doping gives rise to a trapping level capable of compensating silicon‐doped layers. For the first time photoluminescence from a rare earth element incorporated in a III‐V semiconductor has been observed at room temperature.