Band offsets at CdS/CuInS2 heterojunctions are studied by x-ray photoemission spectroscopy. At the CdS/cyanide-treated CuInS2 junction, the conduction band offset is as small as −0.05±0.15 eV, while the valence band offset is 1.18±0.10 eV. The CdS/Cu-rich CuInS2 heterojunction without the treatment, however, possesses a conduction band offset of ∼−0.7 eV. This result suggests that the cyanide treatment improves the interface to give rise to the alignment of the conduction band minima, which is suitable to the solar cell applications.