A semiconductor device includes a support substrate having a first surface capable of supporting the epitaxial growth of at least one III-V semiconductor and a second surface opposing the first surface, at least one mesa positioned on the first surface, each mesa including an epitaxial III-V semiconductor-based multi-layer structure on the first surface of the support substrate, the III-V semiconductor-based multi-layer structure forming a boundary with the first surface and a parasitic channel suppression region positioned laterally adjacent the boundary.