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.