Heterojunction band offsets of GaNAsSb/GaAs, GaInNAsSb/GaAs, and GaInNAsSb/GaNAs/GaAs quantum well (QW) structures were measured by photoreflectance (PR) spectroscopy. These samples were grown by solid-source molecular beam epitaxy using a radio-frequency nitrogen plasma source. PR spectra were collected from the QW structures and the energy transitions were obtained. The experimental data of the QW energy transitions were analyzed by theoretical calculations. Using predetermined values such as QW thickness and composition, unknown factors such as the heterojunction band offsets were able to be determined. For the GaN0.02As0.87Sb0.11/GaAs structure, we found that Qc≈0.5. For Ga0.62In0.38N0.026As0.954Sb0.02/GaAs, we found that Qc≈0.8. This value is similar to the antimony free dilute-nitride material GaInNAs since the small amount of antimony does not affect the band offsets. For the technologically important Ga0.61In0.39N0.023As0.957Sb0.02/GaN0.027As0.973/GaAs laser structure, we found that the GaInNAsSb/GaNAs QW had a conduction band offset of 144 meV and a valence band offset of 127 meV. With a greater understanding of the band structure, more advanced GaInNAsSb laser devices can be obtained.