A field effect transistor (FET) includes a III-nitride channel layer, a III-nitride barrier layer on the channel layer, a first dielectric on the barrier layer, a first gate trench extending through the first dielectric, and partially or entirely through the barrier layer, a second dielectric on a bottom and walls of the first gate trench, a source electrode on a first side of the first gate trench, a drain electrode on a second side of the first gate trench opposite the first side, a first gate electrode on the second dielectric and filling the first gate trench, a third dielectric between the first gate trench and the drain electrode, a second gate trench extending through the third dielectric and laterally located between the first gate trench and the drain electrode, and a second gate electrode filling the second gate trench.