The band lineup of a Ge/ZnSe(100) polar interface has been studied by synchrotron radiation photoemission spectroscopy.Surface sensitive core level spectra indicate that Ge atoms in the overlayer can react with Se atoms at the interface.The valence band offset of this heterojunction has been obtained using core level techniques,and found to be 1.76±0.1eV.The effect of polar surface ZnSe(100) on the valence band offset has been discussed in light of the interface bond polarity model.The experimental results agree well with the theory.