Valence electronic structures of a clean Si(100)-2×1 surface are investigated in a surface-site-selective way using Si- L 23 VV Auger electron–Si-2 p photoelectron coincidence spectroscopy. The Si- L 23 VV Auger electron spectra measured in coincidence with Si-2 p photoelectrons emitted from the Si up-atoms or Si 2nd-layer of Si(100)-2×1 suggest that the position where the highest density of valence electronic states located in the vicinity of the Si up-atoms is shifted by 0.8 eV towards lower binding energy relative to that in the vicinity of the Si 2nd-layer. Furthermore, the valence band maximum in the vicinity of the Si up-atoms is indicated to be shifted by 0.1 eV towards lower binding energy relative to that in the vicinity of the Si 2nd-layer. These results are direct evidence of the transfer of negative charge from the Si 2nd-layer to the Si up-atoms.