The property of electroluminescent porous silicon (PS) diodes as surface-emitting cold cathodes were investigated. The experimental PS diodes consist of thin Au films, PS, n+-type Si substrates, and ohmic back contacts. When a positive bias voltage VPS is applied to the Au electrode with respect to the substrate, electrons are uniformly emitted through the Au contact as well as photons. The cold electron emission characteristics are presented here in terms of the PS layer thickness dependence, effects of rapid thermal oxidation (RTO), and electroluminescence (EL) characteristics. It was demonstrated that both the decrease in the PS layer thickness (dPS) and the introduction of RTO treatment are useful for a significant improvement in the emission characteristics, and that the emission current and efficiency for a RTO-treated diode with dPS=3 μm reach 450 μA/cm2 and 0.2%, respectively, at VPS=27 V. It is also shown that in every case, the Fowler–Nordheim scheme holds in the bias voltage dependence of the emission current. The emission mechanism based on the high-field effect near the outer surface of PS layer, is discussed in relation to the visible EL emission. © 1997 American Vacuum Society.