An interesting case of light emission from a silicon-based device, visible electroluminescence from an Auger phototransistor with a MOS tunnel emitter, has been analysed theoretically. A simple model of this luminescence is developed. The light originating from a tunnel MOS structure is shown to be a superposition of radiation produced by injected hot electrons (HE-radiation) and radiation from the space charge region (SCR-radiation). The shape of the spectrum and the total intensity can be changed by varying the collector voltage and insulator bias. The spectrum of HE-radiation has an apparent high-energy border, whose position depends primarily on the insulator voltage. A substantial contribution to the insulator voltage is provided by holes generated by Auger ionization. (C) 1998 Elsevier Science Ltd. All rights reserved.