High resolution synchrotron radiation photoemission studies of ZnSe-GaAs(110) heterojunctions prepared in situ on atomically clean substrates by low temperature molecular beam epitaxy were conducted using 80-130 eV photons. In addition, the effect of ultrathin Ge interface layers on the band offsets was examined by monitoring the energy separation of the Ga 2p and Zn 2p core levels at the interface with conventional X-ray photoemission spectroscopy. The results indicate that the natural (unmodified) valence band offset for ZnSe-GaAs(110) grown at low temperature is 1.10±0.05 eV, and that the fabrication of a Ge overlayer on GaAs prior to ZnSe deposition yields a decrease in the ZnSe-GaAs valence band offset. The offset decreases monotonically with Ge coverage in the 0.3-4 monolayers range and saturates for Ge thicknesses of 4-6 monolayers. The minimum measured valence band offset that we were able to achieve at the engineered interface is 0.93 ± 0.07 eV.