A process for modifying sections of a semiconductor includes covering the sections to remain free of doping with a metal oxide, e.g., aluminum oxide. Then, the semiconductor is doped, for example, from the gas phase, in those sections that are not covered by the aluminum oxide. Finally, the aluminum oxide is selectively removed again, for example using hot phosphoric acid. Sections of the semiconductor surface which are formed from silicon, silicon oxide or silicon nitride remain in place on the wafer.