The CdS/InP(110) heterojunction, which is one example of a lattice matched combination among the junctions between II–VI and III–V compound semiconductors, was studied on molecular‐beam epitaxy grown samples on cleaved as well as ion bombarded and annealed InP(110) surfaces. The junctions were characterized by core and valence photoemission using synchrotron radiation, Auger electron spectroscopy (AES), and low‐energy electron diffraction (LEED). Deposition of CdS on cleaved InP(110) surfaces led to layers which exhibited good laminar growth, and gave sharp LEED patterns with fairly low background, with a periodicity of the InP(110) substrate lattice, demonstrating that CdS was grown in the metastable zinc‐blende conformation. On InP surfaces cleaned by ion bombardment and annealing, however, growth of crystalline CdS could not be achieved. From the evaluation of band bending upon CdS growth on the basis of core level, line‐shape deconvolution, and the changes in the valence‐band emission, we have derived a valence‐band offset in this system of −0.77±0.1 eV; this means that this heterojunction is of the straddling type, in disagreement with previous data fromC–Vmeasurements which indicated a staggered lineup. We compare our result for the band lineup with current theoretical models.