We have studied the temporal variation of the visible photoluminescence from rapid thermally oxidized porous silicon prepared fromn+substrates. In contrast to the red (slow band) emission, which is observable immediately after high‐temperature oxidation, the blue (fast band) emission is shown to become prevalent only after samples are stored in ambient air. The intensity of the blue emission increases with progressive aging, the magnitude of the increase being dependent on the temperature at which the material is oxidized. Thermal treatment of aged rapid thermally oxidized material can reduce and even quench the blue photoluminescence. Quenching is reversible in that the photoluminescence re‐appears after further aging at room temperature. ©1995 American Institute of Physics.