The donor-cation vacancy complex in Si-doped AlGaAs grown by metalorganic chemical vapor deposition has been identified by examining the growth-condition dependence of photoluminescence (PL) spectra. It has been revealed that the complex has the same origin as the self-activated center in GaAs, and is relevant to the degradation of crystal quality for high doping and high V/III ratio conditions. The excitation intensity dependence of PL spectra, and the fact that the emission is not observed for the samples with indirect gaps, suggest that the emission is a band-to-acceptor transition. The temperature dependence of the emission intensity and linewidth are compared with GaAs.