The room temperature effect of a low dose rate (10-4 rad (Si)/s) 60 Co γ-irradiation on the structural propertiesand dark current of the GaN-based metal-semiconductor-metal (MSM) structure has been studied. In contrast to previous studies, a non-monotonous dependence of the dark current with the γ-irradiation dose is observed. The intensity and linewidth of the photoluminescence (PL) peaks correlate with the changes in electrical characteristics and eventually degrade after prolonged exposure to the γ-radiation. The abnormal behavior of the MSM structure and particularly its I-V and PL characteristics are explained by considering the carrier transfer mechanism in the localized states. These phenomena are associated with the decrease of shallow donors’ density in localized states and the activation of the non-radiative centers as radiation dose increases. These experimental results and the mechanism presented are essential for understanding the interaction of the γ-irradiation with n-GaN and for estimation of reliability of GaN-based (opto)electronics in harsh conditions of γ-radiation (space applications, liquidation of consequences of technogenic catastrophes, etc.).