In a CVD reactor, flushing gases of different heat conductivities are used to flush a gap between a substrate holder and a heating system. The lower side of the substrate holder is configured differently in a central region with respect to the heat transmission from the heating system to the substrate holder, than in a circumferential region that surrounds the central region. The gap has such a gap height that, upon a change of a first flushing gas with a first heat conductivity to a second flushing gas with a second heat conductivity, the heat supplied from the heating system to the substrate holder changes differently in the circumferential region than in the central region.