GaSe1-xSx (0 less than or equal to x less than or equal to 0.5) series layered semiconductor are grown by vertical Bridgman method. Optical properties of GaSe1-xSx (0 less than or equal to x less than or equal to 0.5) crystals are studied using the optical techniques of transmission and piezoreflectance (PzR) measurements. Both the absorption and PzR spectra of GaSe1-xSx series layered semiconductors demonstrate an energy blue-shift behavior with the increase of sulfur composition x in the alloy compounds. Experimental analyses of the optical spectra for GaSe1-xSx with 0 less than or equal to x less than or equal to 0.5 show direct band-gap material for the solid series with photon-energy spectrum ranging from red to green visible region. The compositional dependence of the energy gaps of GaSe1-xSx is analyzed. Broadening parameters for the PzR spectra of GaSe1-xSx compounds are evaluated. The broader PzR line shape of the intermediate compositions in comparing with the binary GaSe compound indicates the presence of stronger alloy scattering effect in the ternary GaSe1-xSx layers. (C) 2004 Elsevier B.V. All rights reserved.