Successful p-type doping of cubic GaN by carbon grown under Ga-rich conditions is reported with maximum hole concentration of 6 × 10 18 cm-3 and hole mobility of 19 cm2/Vs at room temperature, respectively. Cubic GaN:C was grown by rf-plasma assisted molecular beam epitaxy (MBE) on a semiinsulating GaAs (001) substrate (3 inches wafer). C-doping of the c-GaN was achieved by e-beam evaporation of a graphite rode with an C-flux of 1 × 1012 cm-2 s-1. Optical microscopy, Hall-effect measurements and room temperature photoluminescence were used for the investigation of the morphological, electrical and optical properties of cubic GaN:C. Under Ga-rich growth conditions most part of the carbon atoms were incorporated substitutially on N-site giving p-type conductivity. Our results verify that effective p-type doping of c-GaN can be achieved under Ga-rich growth conditions. © 2003 WILEY-VCH Verlag GmbH & Co. KGaA.