Electrical properties of Mg‐doped p‐type GaN grown by metalorganic chemical vapor deposition have been investigated by Hall effect and conductivity measurements. Metastability and persistent photoconductivity effects have been observed in GaN. It was found that at low temperatures, it takes several hours for the free hole concentration to reach its equilibrium value in the dark as well as in the photoexcited state, implying a bistable nature of impurities in p‐type GaN. Temperature dependence of these behaviors have been studied, from which the energy barrier for free hole capture by ionized impurities as well as between the metastable and the stable states of neutral impurities have been obtained.