Steady‐state measurements were made of the optical emission and electrical properties of amphoteric Si‐doped GaAs diodes. The width of the emitting region of these diodes is explained in terms of a theory involving the drift of electrons across a semi‐insulatingp‐region. At low currents radiative recombination occurs in thep‐region within a diffusion length of the junction. However, at high currents a considerable number of injected electrons drift across thep‐region and light emanates from the entirep‐region. The theory is consistent with the observedI‐Vcharacteristics and also with the spreading of the emission into thep‐region.