Power switch devices which base on wide band-gap (WBG) semiconductor, such as silicon carbide metal-oxide-semiconductor-field-effect-transistor (SiC MOSFET) and gallium nitride high-electron-mobility transistor (GaN-HEMT) perform superior performance as compared with silicon (Si) MOSFET in high switching frequency, high blocking voltage, and high temperature operation. In this paper, a series of characteristic test and comparative evaluation of power loss and efficiency which based on Si MOSFET (IPW65R080CFDA), SiC MOSFET (C2M0080120D), and GaN HEMT (TPH3212PS) with similar current rating are conducted in the single-ended flyback converter. It shows that the WBG switch devices can reduce more power loss, improve efficiency, and enhance more power density instead of Si MOSFET.