The aim of the present work is to compare the electronic properties of natural passive films on iron and chromium with sintered bulk metal oxides. The characterization of the semiconductive properties of various bulk oxides shows that the passive film on iron can be simulated by highly doped Fe2O3. The doping concentration of Fe-oxides is determined by their Fe2+ content. At a dopant level of approximate to 5.10(20) cm(-3) in Fe2O3 the flatband potential, bandgap energy, intensity of the photocurrent, and the doping concentration are in good agreement with the natural passive film. A major advantage in using sintered bulk oxides as models for natural passive films is that oxide properties can be separated from effects associated with the underlying substrate. Therefore it could be shown, e.g., that the photocurrent behavior in the case of passive film on iron and chromium is mechanistically determined by interband transitions and is not caused by a photoemission process from the underlying metal. Further, investigations of bulk Fe-oxides revealed that their chemical stability is determined by the Fe2+ content and can be significantly improved by Cr2O3 addition.