The photoluminescence of Ge‐doped AlxGa1−xAs grown by liquid phase epitaxy (LPE) was investigated. The ionization energy of Ge, determined from the photoluminescence spectra, has a strong relation to the Al composition. This cannot be explained by a simple effective mass‐like expression. The broad emission band with a peak at about 1.5 eV, which has been observed by several investigators, was studied further. The intensity of the emission band increased as Ge or as implanted O concentration increased. The peak energy shifted toward higher energy as excitation intensity increased. The paper suggests that this emission band is caused by O donor‐Ge acceptor pair recombination.