An in situ silanization reaction on the surface of freshly prepared porous silicon (PS) has been achieved at room temperature with a trace of amine as the catalyst. Infrared absorption spectra (FTIR) and X-ray photoelectron spectroscopy measurements show that the silanes are successfully attached to the surface of the PS. The effect of the silanization on the stability and the photoluminescence properties of the PS layer has been studied. A mechanism for the silanization reaction based on the alkalinity of the organic amine has been proposed. A new approach for the modification of the surfaces of PS layers by in situ silanization has been established.