Band offsets at the CdS/Cu2In4Se7heterojunction interface were studied by synchrotron radiation soft x‐ray photoemission spectroscopy. CdS overlayers were sequentially grown in steps, at room temperature, on the Cu2In4Se7crystal. Photoemission measurements were acquired after each growth to determine the electronic structure at the heterojunction interface. Results of these measurements indicate that the valence‐band offset &Dgr;Evbmis 1.10(±0.20) eV and that the conduction‐band offset &Dgr;Ecbmis 0.22(±0.20) eV for the CdS/Cu2In4Se7heterojunction. ©1995 American Institute of Physics.