Lattice mismatched 0.5 to 1‐μm‐thick GaAs1−xSbxepilayers were grown on (100)n‐type GaAs by molecular‐beam epitaxy (MBE) throughout the whole composition range and characterized for Sb content up to 0.76. The Sb incorporation coefficient is found to be 0.42 at a substrate temperature of 480 °C. The epilayer quality was examined by x‐ray diffraction, photoluminescence, and photoresponse. The relationship between energy band gap of GaAs1−xSbxand Sb content at room temperature is found to be in good agreement with the result of Nahoryetal. and that at 77 K is established and can be reasonably described by the estimated one from the binary band gaps of GaAs and GaSb at 77 K and the ternary band gaps of GaAs1−xSbxat 300 K. Both majority electron and hole traps in GaAs1−xSbxepilayers were characterized.