Wide Bandgap (WBG) power devices show very good characteristics for high frequency operation in power converters, leading to a better power integration by reducing size and weight of passive components. Access parasitics such as resistances and inductances related to packaging and interconnections are important parameters to determine in order to better predict high frequency switching of WBG power devices. In order to design a 1 MHz hybrid GaN/SiC power converter, this paper reports on the characterization of packaged power devices such as Gallium Nitride (GaN) transistors and Silicon Carbide (SiC) Schottky diodes using S-parameters in order to extract the device parasitics. The method lays on a calibration procedure carried out using specific test fixtures designed on FR4 Printed Circuit Board (PCB). The proposed method has the objective to be suitable for a wide range of power devices.