The structure of amorphousSiOthin film is investigated by means of X‐ray photoelectron spectroscopy. Core electronbinding energies are determined for Si,SiOandSiO2. The problems of charging effects and reference level are discussed. Chemical shifts of Si2p and Si2s electrons are reported for these compounds. ForSiOthe Si photoelectron lines show a doublet structure. It is demonstrated thatSiOis not a mixture of Si andSiO2but may have a definite structure with two unequivalent chemical sites for Si. These ESCA results are interpreted according to the molecular structure model ofSiOsuggested by other physical properties.