In this study, we implemented a depletion (D)-mode gallium nitride high electron mobility transistor (GaN HEMT, which has the advantage of having no body diode) in a class-E amplifier. Instead of applying a zero voltage switching control, which requires high frequency sampling at a high voltage (>600 V), we developed an innovative control method called the minimum power input control. The output of this minimum power input control can be presented in simple empirical equations allowing the optimal power transfer efficiency for 6.78 MHz resonant wireless power transfer (WPT). In order to reduce the switching loss, a gate drive design for the D-mode GaN HEMT, which is highly influential for the reliability of the resonant WPT, was also produced and described here for circuit designers.