New techniques for measuring and analyzing losses in GaN power converters are presented. A 2.4kW synchronous boost converter, switching 300V at 1MHz with normally-off, AlN-base gate, AlGaN/GaN HFETs , serves as a vehicle to substantiate the results. An infrared camera is utilized to accurately measure temperatures of the upper and lower switches, as a function of switched current. These temperature measurements are correlated to loss in the respective switches, utilizing temperature data obtained via DC loss measurements. The higher temperature observed in the lower switch results from the switching loss in that switch, and is clearly evident in the thermal images. Analysis of the temperature dependence exposes the loss due to dynamic on-resistance and the switching loss. The extracted parameters accurately model both the efficiency and junction temperatures versus switching current.