Some embodiments of the present disclosure relate to a HEMT. The HEMT includes a heterojunction structure having a second III/V semiconductor layer arranged over a first III/V semiconductor layer. Source and drain regions are arranged over the substrate and spaced apart laterally from one another. A gate structure is arranged over the heterojunction structure and arranged between the source and drain regions. A first passivation layer is disposed about sidewalls of the gate structure and extending over an upper surface of the gate structure, wherein the first passivation layer is made of a III-V material. A second passivation layer overlies the first passivation layer and made of a material composition different from a material composition of the first passivation layer. The second passivation layer has a thickness greater than that of the first passivation layer.