Cu(In,Ga)S-2 crystals have been grown from the melt using constituent elementary substances as sources. The chalcopyrite structure was confirmed by powder X-ray diffraction patterns. Lattice parameters a and c changed almost linearly corresponding to the composition ratio between In and Ga. The amplitudes of photo-acoustic signals changed greatly near the band gap energies. This phenomenon is due to the changes of the absorption coefficient. Band gap energies, estimated from the photo-acoustic spectra, also showed continuous change with the composition. (C) 2007 Published by Elsevier B.V.