The Si 2p x ray photoelectron spectra of SiO x with a different composition of 0 x 2 have been studied experimentally and theoretically. The SiO x films were prepared by low-pressure chemical vapor deposition from SiH 4 and N 2 O source at 750 C. Neither random bonding nor random mixture models can adequately describe the structure of these compounds. The interpretation of the experimental results is discussed according to a large scale potential fluctuation due to the spatial variation of chemical composition in SiO x. V