A comprehensive model for the metastable defects in a‐Si:H is developed by adapting a recent theory for several kinds of defects in crystalline semiconductors, particularly the DX center in AlGaAs. This new model accounts in a unified way for all of the major observations of defects induced by light, quenching, doping, or compensation; as well as for their anneal. The stretched‐exponential time dependence of defect densities with light or annealing, and saturation of the density are also explained. This model is based on foreign atoms rather than on Si‐Si bond breaking, and in undoped materials it is suggested that uncontrolled impurities are the source.