The objective of the proposed work was to investigate the electrical performance of a 250 µm-thick 4H-SiC p-n junction detector after irradiation with DT neutrons (14.1 MeV energy) at high temperature (500 °C). The results showed that the current–voltage (I-V) characteristics of the unirradiated SiC detector were ideal, with an ideality factor close to 1.5. A high electron mobility (µn) and built-in voltage (Vbi) were also observed. Additionally, the leakage current remained very low in the temperature range of 298–523 K. High-temperature irradiation caused a deviation from ideal behaviour, leading to an increase in the ideality factor, decreases in the µn and Vbi values, and a significant rise in the leakage current. Studying the capacitance–voltage (C-V) characteristics, it was observed that neutron irradiation induced reductions in both Al-doped (p+-type) and N-doped (n−-type) 4H-SiC carrier concentrations. A comprehensive investigation of the deep defect states and impurities was carried out using deep-level transient spectroscopy (DLTS) in the temperature range of 85–750 K. In particular, high-temperature neutron irradiation influenced the behaviours of both the Z1/2 and EH6/7 traps, which were related to carbon interstitials, silicon vacancies, or anti-site pairs.