Electronic defects in MOCVD-grown n-type GaN were characterized by conventional deep level transient spectroscopy (DLTS) and by photoemission capacitance transient spectroscopy (O-DLTS) performed on Schottky diodes. With DLTS two deep levels were detected with thermal activation energies for electron emission to the conduction band of 0.16 eV and 0.44 eV. With O-DLTS we demonstrate four new deep levels with optical threshold energies for electron photoemission of ∼ 0.87 eV, 0.97 eV, 1.25 eV and 1.45 eV. The O-DLTS apparatus and the measurement are discussed in detail. We also report characterization of the Au-GaN barrier height of the Schottky diode by internal photoemission.