I. Introduction
Conversion losses are responsible for more than 10 % of global electricity consumption; in terms of efficiency, the transistor is one of the most critical components of a power converter. Resistive losses related to the on-resistance of the device, and switching losses related to the charging/discharging of the parasitic capacitances can be reduced only through the design of optimized devices, based on innovative semiconductor materials. Over the last few years, gallium nitride (GaN) has emerged as an excellent material for the fabrication of efficient power converters: the high electron mobility of the bi-dimensional electron GaN allows to minimize the on-resistance (Ron) of high-electron mobility transistors. In addition, the low (on-resistance)x(gate charge) product permits to significantly reduce the switching losses compared to conventional silicon devices.