Angular correlation measurements on the fcc solid solutions of Cu-Ge and Cu-Si alloys have been carried out on single crystals with four crystallographic orientations by a crossed-slit geometry. The results on both the alloys are nearly the same. The -neck radius and the -radius of the Fermi surfaces increase almost linearly with increasing electron concentration in accord with previous results on Cu-Al and Cu-Zn alloys. The Fermi surface does not touch the square faces of the Brillouin zone at the solubility limit. The results agree fairly well with a calculation based on the sinking-conduction band model
