The steady‐state defect density in hydrogenated amorphous silicon (a‐Si:H) under illumination was investigated for a wide range of illumination intensities and temperatures. The saturation defect density under illumination is both temperature and light intensity dependent. A chemical equilibrium model for light‐induced defect generation is proposed. According to the model, defect generation is enhanced under illumination due to the reduction of the defect formation energy when the bands are populated by photogenerated carriers. Defect generation is a self limiting process and the defect density reaches a saturation value at long illumination time despite the existence of an extended distribution of defect formation sites.