Abstract: A GaN HEMT structure having: a first III-N layer on GaN; a source electrode in contact with a first surface portion the first III-N layer disposed over a first region in the GaN layer; a drain electrode in contact with a second surface portion of the first III-N layer disposed over a second region in the GaN layer; a gate electrode disposed over a third surface portion of the first III-N layer, such third surface portion being disposed over a third region in the GaN layer. The GaN layer has: a fourth region therein disposed between the first region therein and the third region; and a fifth region therein disposed between the third region therein and the second region therein. A second III-N layer is disposed over the first III-N layer for generating a two-dimensional electron gas density in the GaN density in at least one of the fourth region and fifth region greater than the density in the third region of the GaN layer.