Photoluminescent and electroluminescent properties of porous silicon layers were studied at different oxidation times after application of anodic current transients. Changes in the wavelength and intensity of the emitted photoluminescence could be explained as the consequence of a gradual electrooxidation of silicon structures. Also, the time delay associated with the recording of electroluminescence was interpreted as being due to the oxidation of bulk silicon by holes injected by the power supply. Once bulk silicon becomes oxidized, holes can reach the valence band of silicon microstructures where quantum size effects lead to visible light emission.