The SiC/Si hybrid switch has been reported as a natural next step moving forward for high voltage applications to address the high cost issue of SiC devices. However, the existing gate control strategies of the SiC/Si hybrid switch focus on decreasing the total power loss, which induces a serious concern of the SiC MOSFET’s overheating and reliability degradation in the hybrid switch. In order to solve these issues, a dynamic thermal controller is proposed for power switching devices inside the SiC/Si hybrid switch to prevent them from overheating and keep the thermal balance between the two switching devices simultaneously. The proposed control method utilizes the turn-off delay time between the gate signal of the SiC MOSFET and Si IGBT to balance the junction temperature between the two devices and keep them from overheating. A 20 kHz DC/DC buck converter which is based on SiC/Si hybrid switch is developed and tested to validate the proposed active thermal control technique. Experimental results demonstrate that the SiC/Si hybrid switch with the proposed control method can accomplish a much lower junction temperature than that with the existing gate control mode in the same output power rating, and a larger output power capability in the DC/DC buck converter.