X‐ray photoelectron spectroscopy (XPS) and Si K‐edge x‐ray absorption near‐edge spectroscopy (XANES) have been used to characterize 0.5–20 nm thick SiO2films on Si(100). In XPS measurements, the chemical shift of the Si(‐O) 2ppeak increases with oxide thickness. However, by neutralizing the surface with low‐energy electrons, and using the C 1sas a reference, a chemical shift of 3.9±0.1 eV is found for neutralized oxide films, and the energy difference between the O 1sand Si(‐O) 2pis independent of oxide thickness. XANES measurements confirm an invariant chemical shift with oxide thickness, the SiKedge from SiO2being 1845.50±0.05 eV for all samples. XPS and XANES data then clearly show that any change in chemical shift of the Si(‐O) 2pwith oxide thickness is mainly due to a surface charging rather than microscopic strain induced by the molar volume mismatch between the oxide and the substrate, as has been previously believed.