In this work, the effects of 60Co γ-ray irradiation on high resistivity p-type diodes have been investigated. The diodes were exposed to dose values of 0.1, 0.2, 1, and \SI2{\mega Gy}. Both macroscopic (I--V, C--V) and microscopic (Thermally Stimulated Current~(TSC)) measurements were conducted to characterize the radiation-induced changes. The investigated diodes were manufactured on high resistivity p-type Float Zone (FZ) silicon and were further classified into two types based on the isolation technique between the pad and guard ring: p-stop and p-spray. After irradiation, the macroscopic results of current-voltage and capacitance-voltage measurements were obtained and compared with existing literature data. Additionally, the microscopic measurements focused on the development of the concentration of different radiation-induced defects, including the boron interstitial and oxygen interstitial (BiOi) complex, the carbon interstitial and oxygen interstitial CiOi defect, the H40K, and the so-called IP∗. To investigate the thermal stability of induced defects in the bulk, isochronal annealing studies were performed in the temperature range of \SI{80}{\celsius} to \SI{300}{\celsius}. These annealing processes were carried out on diodes irradiated with doses of 1 and \SI2{\mega Gy} and the corresponding TSC spectra were analysed. Furthermore, in order to investigate the unexpected results observed in the C-V measurements after irradiation with high dose values, the surface conductance between the pad and guard ring was measured as a function of both dose and annealing temperature