Spectral ellipsometry is a widely used method for analysing optical properties of materials. In particular electronic interband transitions of many semiconductor materials have been intensively studied employing ellipsometry from the near-infrared to the ultra-violet (UV) spectral range. Electronic excitations involving core-levels, on the other hand, have been a domain of synchrotron based X-ray absorption spectroscopy or electron loss spectroscopy. We apply spectral ellipsometry in the vacuum-UV spectral range to study core level excitations in GaN. The results proof that VUV-ellipsometry is a very versatile tool to obtain information on the p-like component of the density of states (DOS) related to the conduction bands of GaN. Excitations of the 3d core level of Ga are shown to be linked to the partial DOS at the Ga site within the lattice (complementary to the information obtained on nitrogen sites by X-ray absorption at the N1s edge). (© 2005 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)