In order to manufacture an epitaxial wafer having satisfactory flatness over its entire surface, epitaxial layers are experimentally grown upon actual wafer samples under various different layer formation conditions, the thickness profiles are measured over the entire surfaces of these wafers before and after growth of the layers, and, from the differences thereof, layer thickness profiles over the entire areas of the epitaxial layers under the various different layer formation conditions are ascertained and stored. Thereafter, the thickness profile of a substrate wafer is measured over its entire area, this is added to each of the layer thickness profiles under the various different layer formation conditions which have been stored, and the planarities of the manufactured wafers which would be manufactured under these various different layer formation conditions are predicted. And one set of processing conditions is selected which is predicted to satisfy a required flatness specification, and an epitaxial layer is actually grown upon the substrate wafer under these processing conditions.