In this work, a 26.5 GHz to 29 GHz GaN MMIC Doherty power amplifier concept with two stages per path is investigated in a 150 nm GaN HEMT MMIC technology. Prior to the design the placement of driver stages in Doherty amplifiers is studied and their influence on the system efficiency is evaluated. One of the key findings is that a gain in the second stage of 15 dB assures a degradation on system drain efficiency of less than 5 % in comparison to the single stage efficiency of the second stage. The fabricated GaN Doherty amplifier exhibits a maximum power added efficiency of 35 % and maximum backoff efficiency of 24 % at 8 dB backoff while maintaining a saturated output power of 30.4 dBm.