The chemical composition of ultrathin oxide–nitride–oxide multilayer films grown onto p-type silicon substrates and subjected to different annealing processes and to various oxidation times of the nitride layer has been studied by means of x-ray photoelectron spectroscopy and time-of-flight–secondary-ion-mass spectroscopy. Our results show that the annealing process strongly influences the bottom SiO 2 /Si interface allowing the saturation of the dangling bonds present at this interface and decreasing the concentration of free hydrogen. By increasing the oxidation time, a better silicon dioxide layer is formed in the topmost layer of this structure. © 1997 American Vacuum Society.