The junction formation of polycrystalline CuInSe2 absorbers (CIS) with thermally evaporated CdS was investigated by high-resolution synchrotron X-ray photoelectron spectroscopy. The chemistry and electronics of the interfaces of Cd partial electrolyte treated CIS ('' wet '' processed) and clean, decapped CIS ('' dry '' processed) were compared. A valence band offset of 0.96(10) eV was determined in both cases. The Cd (Se,OH) surface layer induced by the wet Cd partial electrolyte process does not significantly modify the band alignment at the CIS/CdS heterointerface from the '' dry '', vacuum-processed CIS/CdS interface. During the stepwise interface formation the energy converting capability of the CIS/CdS heterojunction was assessed by in situ surface photovoltage measurements at room temperature. The evolution of the surface photovoltage significantly differs for the '' wet '' and the '' dry '' interfaces and is discussed in relation to the function in solar cell devices. (C) 2006 Elsevier B.V. All rights reserved.