GaN HEMTs have been gaining popularity in power electronics applications due to their advantages with respect to silicon power transistors, such as higher speed, lower ON resistance, larger breakdown voltage and smaller size. Driving this new generation of power transistors, however, presents some challenges: the large slew rates (for both voltage and current) associated with high-speed operation can lead to EMI and voltage oscillations. When it comes to gate voltage range, GaN HEMTs have stricter requirements compared to silicon power transistors, which means that these voltage oscillations can either inadvertently turn-on the device or outright damage it. This thesis focuses on how to detect voltage oscillations after the turn-off of the GaN device through the use of a CMOS comparator built into the active gate driver.