The electronic structures of PTCDA on the Sn/Si(111)-2√3×2√3 surface have been thoroughly studied by high-resolution photoelectron spectroscopy and near-edge X-ray absorption fine structure (NEXAFS). Upon deposition of PTCDA, there is an unusual charge transfer from the Sn/Si(111)-2√3×2√3 surface to the molecules. This is clearly shown by a new component in the Sn 4d core-level spectra that shifts towards higher binding energy. In contrast to the literature, the charge provided by Sn is donated to the carbonyl C instead of the O atoms. This is revealed by a new component in the C 1s core-level spectra that shifts towards lower binding energy. The charge transfer causes a splitting of the HOMO level in the valence band spectra. As indicated in the NEXAFS spectra, it also induces a splitting of the LUMO level of the molecules. For thick films the NEXAFS results suggest a layer by layer growth mode.