Thin films of 200 nm of VO_x RF magnetron sputtered on the SiO₂ glass and Si substrates were studied with X-ray Absorption Spectroscopy in the XANES range of the oxygen K and vanadium L_2,3 edges. The total electron yield (TEY) detection mode was used. The spectra were collected at several temperatures between room temperature and 300 °C for the unpolarized and linearly polarized beam to study polarization effects. The experimental data were compared with the theoretical model based on DFT-ROCIS (Density Functional Theory, Restricted Open shell Configuration Interaction with Singles) from the literature. Changes in the spectra with temperature, particularly visible at the oxygen K edge are attributed to the loss of surface oxygen and the corresponding changes of population of the single- double- and triple vanadium coordinated oxygen. The corresponding decrease of the surface stoichiometry leads to formation lower than V⁵⁺ valency of vanadium ions such as V⁴⁺ or V³⁺ i.e., containing d-electrons. It gives a tentative explanation for the occurrence of metallicity attributed in the literature to a metal–insulator transition (MIT).