The temperature dependence of the energy gaps for sulfur‐annealed copper indium disulfide has been studied by photoreflectance in the temperature range of 10–300 K. The sulfur‐annealed sample has been found to have larger transition energies, smaller positive temperature coefficients of energy gaps, and larger spin‐orbit splitting energy than the as‐grown sample. This can be explained by the reduction ofd‐level contributions in the upper valence band probably caused by the variation of lattice distance due to native defects.