The blocking voltage level of silicon carbide (SiC) can reach 10–25 kV, which will significantly increase the power density and capacity of power modules. However, high voltage can induce a high electric field, increase the risk of partial discharge (PD), and threaten the insulation reliability. This paper focuses on the triple points between the metal electrode, silicone gel, and ceramic in power modules. The influencing factors of the electric field at different triple points are fully analyzed. PD experiments are performed and the results show that the interface between silicone gel and ceramic is a weak area of insulation. Therefore, this paper demonstrates that area of weak insulation and high electric field meet at the triple point. To solve this problem, a new structure of the ceramic substrate is proposed, which isolates the interface area from the high electric field. At the same time, the new structure can significantly reduce the high electric field reinforcement.