In some examples, a transistor comprises a gallium nitride (GaN) layer; a first GaN-based alloy layer having a top side and disposed on the GaN layer; a second GaN-based alloy layer disposed on the first GaN-based alloy layer, wherein the second GaN-based alloy layer covers a first portion of the top side; and a source contact structure, a drain contact structure, and a gate contact structure, wherein the source, drain, and gate contact structures are supported by the first GaN-based alloy layer.