This paper presents a frequency compensation scheme of the first, to the authors\' knowledge, full GaN operational amplifier. The amplifier is based on a previous topology originally developed for nMOS technology and here adapted for a modern GaN process. The solution is able to drive a capacitive load as high as 1 nF and a suitable design strategy has been developed. The operational amplifier exhibits a very high nominal DC gain of about 135 dB, a unity-gain bandwidth of about 560 kHz with 60° phase margin, a slew rate of about 0.83 V/us and a nominal quiescent current consumption of 200 uA from a 6-V supply.