Abstract The visible luminescence of porous silicon electrodes is reported. Both n-type and p-type material show similar characteristics. Three potential ranges can be distinguished. At open-circuit potential in the presence of certain strong oxidizing agents, e.g. Ce 4+ and MnO - 4 , emission due to chemiluminescence (CL) occurs. At negative potential in the range of H 2 evolution, hole injection by a strong oxidizing agent, e.g. H 2 O 2 and S 2 O 2- 8 , results in electroluminescence (EL). The intensities of CL and EL depend on the applied potential. When porous silicon is anodically oxidized, emission also occurs; this is probably due to CL. Because of the close resemblance of the luminescence of porous silicon to the photo- and chemiluminescence of siloxene, the emission from porous silicon is ascribed to the presence of siloxene or siloxene-like groups. The porous layer can be described as a discrete semiconductor with a large band-gap.