We report the first demonstration of visible light emission from an all solid-state n-p heterojunction diode based on porous silicon. The p-type silicon was electrochemically etched in a hydrofluoric acid solution to form a porous silicon region; the n-p heterojunction diode was fabricated by depositing a wide bandgap n-type semiconductor, indium-tin-oxide (ITO), onto the surface of the porous silicon. With positive bias applied, electroluminescence was observed with a relatively narrow peak at about 580 nm. The device showed strong rectifying properties and no light emission was observed under reverse bias condition. Photoluminescence in the red, orange, yellow, and green was also observed in separate sample preparations.