We have developed new isolated gate drivers using what we call Drive-by-Microwave technology that enables wireless power transmission of input signals. In order to realize the compactness of the gate driver and to obtain isolated gate signals with enough power to directly drive the switching power devices, we have developed a novel compact butterfly-shaped electro-magnetic resonant coupler (EMRC) that operates with RF converted input signals at 5.8GHz. By integrating this EMRC, one-chip GaN isolated gate driver ICs on a sapphire substrate have been developed and their direct driving of the GaN-GIT power switching devices was successfully demonstrated.