This method for assaying copper in silicon wafers includes the steps of: forming a polysilicon layer on the surface of a p-type silicon wafer having the same characteristics as the silicon wafers being assayed; heat treating the p-type silicon wafer after it has been polished; dissolving the polysilicon layer on the heat-treated p-type silicon wafer with a mixed acid composed of at least hydrofluoric acid and nitric acid; and quantitatively determining the copper components within the mixed acid following dissolution of the polysilicon layer.