Thin films of pure vanadium oxide (VOx) and Ge doped vanadium oxide (VOx:Ge) have been deposited by reactive magnetron sputtering on Si (100) substrates. These films were characterized by means of in situ X-ray photoelectron spectroscopy and ultraviolet photoelectron spectroscopy to address the doping induced changes in the core-level and valence-band spectra of the material. Doped films exhibit a decrease in the density of states at the Fermi level, indicating the insulating character of said films compared with the undoped ones. Doped vanadium dioxide is a promising candidate for switchable absorber coatings for solar thermal collectors. Copyright (c) 2016 John Wiley & Sons, Ltd.