Mg doping was attempted in (1 (1) over bar 01)GaN grown on a patterned (001)Si by selective metal-organic vapor phase epitaxy (MOVPE). The source material for the Mg doping was EtCp2Mg and the electrical properties were studied on samples with different doping levels. All samples showed p-type conduction. However, the hole concentration was decreased by the Mg doping at low doping levels followed by an increase at high doping levels. The activation energy was around 106-130 meV depending on the doping level, which was larger than that found in undoped or carbon-doped samples. The AFM images showed gradual change in the surface structure in accordance with the Mg-doping level. The variation of the optical spectra was discussed in relation to the Mg-doping levels. (c) 2006 Elsevier B.V. All rights reserved.