Interfacial reactions between Ni, Pd, or Au contacts and AlxGa1-xN with compositions x = 0.15 and 0.47 were studied in this investigation. X-ray photoelectron spectroscopy and scanning transmission electron microscopy coupled with energy dispersive spectroscopy showed that reaction between these metals and AlxGa1-xN results in a pronounced shift in the AlxGa1-xN beneath the contact to an Al-enriched composition. This Al enrichment results from the preferential outdiffusion of Ga into the metal films, and this reaction is consistent with thermodynamic driving forces in these systems. Possible consequences of the observed compositional shift on the electrical properties of contacts to AlxGa1-xN are also discussed. (C) 2004 American Vacuum Society.