A hybrid cascoded GaN switch configuration is demonstrated in power conversion applications. A novel metal package is proposed for the packaging of a D-mode GaN metal-insulator-semiconductor high electron mobility transistor (MIS-HEMT) cascoded with an integrated power MOSFET and a Schottky barrier diode. The normally-off cascode circuit provides a maximum drain current of 14.6 A and a blocking capability of 700 V. Analysis of 200 V/ 1 A power conversion characteristics are discussed and show the excellent switching performance in load circuits. Switching characteristics of the integral SiC Schottky barrier diode are also demonstrated. Finally, a flyback AC-DC converter is used to evaluate the benefit of GaN cascode switches. These results show that high-voltage GaN-HEMTs can be switching devices for an ultralow-loss converter circuit.