A novel 650 V/50 A 4H–SiC junction barrier Schottky diode (JBSD) featuring a stripe-square composite cell design (SSC-JBSD) is proposed in this paper to improve the high-temperature performance. A model of the resistance of the JBS (RJBS) is established to explain the mechanism. The particular cell design of the SSC-JBSD forms a circular current distribution, which can improve the forward current and suppress the degeneration of RJBS caused by the lower electron mobility at high temperatures. The combination of the stripe and square P+ regions achieves a high current and a lower power loss under high temperature while maintaining a high breakdown voltage. Specifically, the power loss of the SSC-JBSD with a forward current of 50 A only increases by 6.9 % under 450 K compared to that under 300 K, while that of the conventional JBS diode (Conv-JBSD) increases by 14.1 %. And the Baliga figure of merit (FOM) of the SSC-JBSD is 15.6 % higher than that of the Conv-JBSD under a temperature of 450 K. The on-state self-heating measurement shows that the temperature of the SSC-JBSD is approximately 30 K lower than that of the Conv-JBSD after 5 s of constant on-state operation with a forward current of 50 A. The proposed SSC-JBSD demonstrates superior performance at high temperatures, making it an available replacement for Conv-JBSD in harsh environments characterized by high temperatures and large currents.