Using electrochemical and in situ luminescence measurements we show that ferricyanide ions are reduced at n-type ZnSe electrodes by hole injection into the valence band of the semiconductor. At negative potentials the holes recombine with electrons and electroluminescence is observed. At the open-circuit potential, the injected holes are used for the oxidation and dissolution of the semiconductor. This electroless etching reaction is under mixed diffusion/kinetic control at 20 degrees C, but becomes diffusion controlled at higher temperature.