Semiconductor wafers composed of silicon with an epitaxially deposited layer, are prepared by: placing a dummy wafer on a susceptor of an epitaxy reactor; conducting an etching gas through the epitaxy reactor in order to remove residues on surfaces in the epitaxy reactor through the action of the etching gas; conducting a first deposition gas through the epitaxy reactor in order to deposit silicon on surfaces in the epitaxy reactor; replacing the dummy wafer by a substrate wafer composed of silicon; and conducting a second deposition gas through the epitaxy reactor in order to deposit an epitaxial layer on the substrate wafer.