Abstract: Thermal annealing effects of a GaAs0.909Sb0.07N0.021 film grown on GaAs substrate via gas-source molecular beam epitaxy have been characterized by photoluminescence (PL) and photoreflectance (PR) techniques. PL measurements show the evolution of luminescence feature with the thermal annealing treatment. The conduction to heavy-hole (HH) band and conduction to light-hole (LH) band transitions originated from the strained induced valence band splitting in GaAs0.909Sb0.07N0.021 layer have been observed by the PR measurements. The near band edge transition energies are slightly blueshifted, and the splitting of HH and LH bands is reduced with rising annealing temperature. The temperature dependences of near band edge transition energies are analyzed using Varshni and Bose–Einstein expressions in the temperature range from 15to300K. The parameters that describe the temperature variations of the near band edge transition energies are evaluated and discussed.