In aerospace applications, it is important to have efficient, small, affordable, and reliable power conversion units with high power density to supply a wide range of loads. Use of wide-band gap devices, such as Silicon Carbide (SiC) and Gallium Nitride (GaN) devices, in power electronic converters is expected to reduce the device losses and needs for extensive thermal management systems in power converters, as well as facilitate high-frequency operation, thereby reducing the passive component sizes and increasing the power density. A novel hybrid SiC-GaN based full-bridge dc-dc buck converter with improved efficiency for high power applications will be presented in this paper. With the current device manufacturing technology, GaN devices can only handle breakdown voltages up to 650 V, while SiC devices can handle up to 1200 V. GaN devices exhibit remarkable switching performance compared to SiC devices. This work aims to exploit both the high voltage capability of SiC devices and exceptional switching capability of GaN devices to improve the overall converter performance, by using SiC devices in the high-voltage primary side and GaN devices in the low-voltage secondary side. A 10 kW, 150 V full-bridge dc-dc buck converter with an input voltage 400 V ≤ VI ≤ 660 V operating in CCM at a switching frequency of 200 kHz will be designed and simulated using LTSpice circuit simulator. Simulation results will be presented for (1) SiC based (2) GaN based and (3) hybrid SiC-GaN based converter. As expected GaN based converter exhibited superior performance with an efficiency of 99 %. However, using only GaN devices is not a choice because of the high voltage stresses in the primary side. The proposed hybrid SiC-GaN based converter exhibited better performance compared with that of SiC based converter with a 1% increase in efficiency and lower switching transition times.