The chemical nature of the GaN surface combined with the bulk and surface electronic structure opens new potential application areas for this material. The nature of specific organic-GaN was developed for two cases in which the surface electronic structure of such interfaces was developed and utilized. The band alignment between n-GaN and pentacene was determined for surfaces prepared through reaction with HCl. The energy band offset was estimated through combined X-ray photoelectron spectroscopy and ultraviolet photoemission measurements. XPS measurements indicated that there was no interfacial chemical reaction. The measured valence band offset between the n-GaN and the vapor-deposited pentacene was estimated to be greater than 2 eV providing a favorable band-offset for hole-injection from the GaN layer into pentacene. The surface of a AlGaN/GaN heterojunction field effect transistor (HFET) structures was also functionalized by an adsorbed hemin layer and was shown to be sensitive to the presence of reactive species such as NO. The HFET structure provides enhanced sensitivity to changes in the surface electric field, altered through the adsorption of chemically active species either directly on the surface or through the interactions with surface functionalization. (c) 2006 Elsevier B.V. All rights reserved.