Deep centers in undoped n-GaN grown by Hydride Vapor Phase Epitaxy were characterized by Deep Level Transient Spectroscopy (DLTS), revealing four known levels with activation energies in the range 0.17-0.94 eV. Deeper levels in the bandgap were observed by photocapacitance (PHCAP) experiments. A correspondence can be established for the dominant DLTS level observed both by thermal and optical experiments, exploiting the temperature as a key parameter in PHCAP measurements. The Franck-Condon shift d(F-C) for this level was estimated around 0.33 eV, in close agreement with results obtained by Hacke and coworkers in a more elaborate way. The tentative assignment of most levels is discussed on the basis of literature, pointing out unsettled origins for some of them. (c) 2005 WILEY-VCH Verlag GmbH D Co.