The alkali antimonide compounds are widely applied in light detection devices. The strong optical absorption and the low electron affinity make the photon-electron conversion very efficient in these materials. In this paper, we present the results of a photoemission spectroscopy study of K3Sb films of 100 Angstrom with and without an extra layer of 0.1 ml Cs. The shallow Sb 3d core levels show a chemical shift for K3Sb, which is only very slightly affected by the extra Cs layer. The results are explained as a consequence of charge accumulation at the K3Sb surface, which is induced by the Cs surface states.