A field effect transistor (FET) includes source and drain electrodes, a channel layer, a barrier layer over the channel layer, a passivation layer covering the barrier layer for passivating the barrier layer, a gate electrode extending through the barrier layer and the passivation layer, and a gate dielectric surrounding a portion of the gate electrode that extends through the barrier layer and the passivation layer, wherein the passivation layer is a first material and the gate dielectric is a second material, and the first material is different than the second material.
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