The reactivity at the Mo/SiO2 interface is studied as a function of the method of preparation of the silica layer. Three preparation methods for the silicon substrate are considered: plasma-enhanced chemical vapor deposition, and wet and dry thermal oxidations. Respective hydrogen contents in the silica layer of 3.4, 0.5, and 0.4 at. % are induced. We report on the formation of molybdenum silicides (MoSi2 and Mo5Si3) at the Mo/SiO2 interfaces from an x-ray emission spectroscopy study of the interfacial Si 3p occupied valence states. The interfacial reactivity increases with the hydrogen content of the silica film, which is explained by the ease with which the Si-H bonds break during the early stage of the deposition of the metal by cathodic sputtering. (c) 2005 American Institute of Physics.