Self-powered flexible thermal-management systems have garnered interests in wearable electronic devices and AI semiconductors. However, their efficiency and reliability remain limited in practical applications. In this study, an ionic temperature-sensing triboelectric nanogenerator (iTS-TENG) is proposed with an ionic elastomer containing thermoplastic polyurethane (TPU) and ionic liquids (ILs). The TPU matrix undergoes deformation of microphase separation by thermal stimulation near the glass transition temperature. Furthermore, ILs facilitate the formation of electrical double layers as charge carriers and enhance the thermal sensitivity as heat carriers under mechanical and thermal stimuli. Thus, iTS-TENG demonstrates enhanced outputs (734 V) and high thermal sensitivity (3.87 V/°C) from room temperature to 70 °C, with fast response time and reproducibility (more than 20 cycles). Finally, real-time and self-powered iTS-TENG is demonstrated, showing that the sensed temperature is comparable to a commercial temperature sensor. These results indicate that iTS-TENG is suitable for thermal-management applications in self-powered wearable electronic systems.