In some embodiments, the present disclosure relates to a high voltage device that includes a substrate comprising a first semiconductor material. A channel layer that comprises a second semiconductor material is arranged over the substrate. An active layer that comprises a third semiconductor material is arranged over the channel layer. Over the active layer is a source contact spaced apart from a drain contact. A gate structure is arranged laterally between the source and drain contacts and over the active layer to define a high electron mobility transistor (HEMT) device. Between the gate structure and the source contact is a cap structure, which is coupled to the source contact and laterally spaced from the gate structure. The cap structure and a gate electrode of the gate structure comprise a same material.