The behaviors of Ga and N vacancies (Schottky defects, Frenkel defects), lattice-site and interstitial Mg atoms, and interstitial H atoms have been studied in the wurtzite-type GaN crystal by molecular dynamic simulation. The diffusivity of interstitial Mg atoms on the (0001) plane is predominant compared with the diffusivity along the [0001] direction. Diffusion coefficients of interstitial Mg atoms are composed of two Arrhenius formula for temperatures from 850 K to 2000 K. The one reflects the high-possibility occurrence of jumping movements among cage centers of hexagonal crystal structure for higher temperature. The other reflects the thermal vibration at the cage center for lower temperature. (C) 2003 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.