AbstractElectron spectroscopy investigations of anodic silicon oxides grown over monocrystalline silicon and obtained at room temperature under different oxidation conditions are discussed and compared with thermal silicon oxide. In the first place, XPS shows that these oxides are essentially similar to thermal oxides with the same band gap, valence band spectra, plasma frequency, charge transfer and bulk mass density. However, there are also some important differences with respect to thermal oxides, related to the large density of structural defects, mainly OH and H2O, incorporated in the lattice during the growth process. In spite of the SiO2/Si interface appearing to be locally abrupt, this interface seems to be very rough. The anodic oxides have some oxygen excess and consequently the electronic polarizability of such materials is slightly smaller than that of thermal oxides. However, the most striking difference is the build‐up of a surface potential of 1.4–3.3 V upon x‐irradiation, even for thin, low‐resistivity anodic oxide films.