Abstract: A GaN transistor with reduced output capacitance and a method form manufacturing the same. The GaN transistor device includes a substrate layer, one or more buffer layer disposed on a substrate layer, a barrier layer disposed on the buffer layers, and a two dimensional electron gas (2DEG) formed at an interface between the barrier layer and the buffer layer. Furthermore, a gate electrode is disposed on the barrier layer and a dielectric layer is disposed on the gate electrode and the barrier layer. The GaN transistor includes one or more isolation regions formed in a portion of the interface between the at least one buffer layer and the barrier layer to remove the 2DEG in order to reduce output capacitance Coss of the GaN transistor.