First observation of light emission due to negative differential resistance in a new optoelectronic device called an optoelectronic triangular barrier switch, which displays bistable electrical characteristics, is reported. The light emission is shown to be initiated by controlled reverse breakdown and then sustained by avalanching for the duration of the negative differential resistance part of the device electrical characteristics. The spectral content was measured and has peak emission at 0.85 &mgr;m, which corresponds to the band‐gap energy of the GaAs. It is shown that the light emission is due to the radiative recombination of electron‐hole pairs created by avalanching electrons and not due to the recombination of high‐energy electrons and holes.