The valence electron states at the Si(111)(2×1)/Yb interface are discussed in terms of the Si L 2,3 VV Auger lineshape. The existence of Si 3p/Yb 5d interaction is inferred on the basis of strong similarities observed between the Si L 2,3 VV lineshapes of the interface reaction products and those of Ca silicides. Detailed spectroscopic assignments in the distribution of the valence states are made possible by comparing the experimental spectra to theoretical calculations performed within the LMTO-ASA scheme.