A novel catalytic reaction using a trace of organic amine as the catalyst enables hydrolysis of the silicon–hydrogen groups on the fresh prepared porous silicon (PS), generating the hydroxyl-terminated surfaces without extensive oxidation of the Si–Si backbonds. The reactivity of the hydroxyl-terminated surfaces with various silanization reagents was investigated, which proceeds by abstraction of the surface –OH to form an organic monolayer of Si–O–Si–C bonds and importantly retains the intrinsic structural properties of the PS layers. Furthermore, an in situ silanization modification of the silicon–hydrogen surfaces has been established. Stability testing shows that the resulting organic monolayers are densely packed and are shown to be highly stable under a variety of conditions including hot water, hot organic solvent, acid, and base, but can be removed by a HF rinse.