There are several applications where solid devices are exposed to irradiation. Depending on the operational conditions (type of the particles, temperature, fluence) the physical properties of the exposed device degrades differently, reaching the point of electrical failure in very harsh enviroments. The radiation damage, starting already under low irradiation fluences, get more complex with increasing fluences due to the generation of various type of irradiation induced, electrically active, defects. Accordingly, the defect characterization becomes a more difficult and costly task, requiring several complementary techniques to understand the detailed relation between the “microscopic” reasons as based on defect analysis and their “macroscopic” consequences for device performance. In this respect, we present the most powerful techniques employed and developed within the CERN RD50 Collaboration for investigating highly irradiated materials/structures: (i) Thermally Stimulated Current and Thermally Dielectric Relaxation Current techniques used for electrical characterization of bulk and interface defect states. With the obtained defect parameters several electrical characteristics of the devices could quantitatively explained; (ii) High Resolution Transmission Electron Microscopy and Electron Paramagnetic Resonance allowing the structural and chemical identification of the radiation induced defects.