The atomic arrangement of NiAu contacts on p -type GaN has been studied by transmission electron microscopy (TEM). The initial AuNiGaN structure transforms upon annealing at 400-600°C into NiAuGaN. The Au layer consists of thin platelets with uniform thickness. High-resolution TEM reveals an atomically sharp interface between GaN and Au, with no intermediate phases present. The epitaxial relationship between the Au layer and the GaN film is (111) Au∥ (0002) GaN, and [1 1- 0] Au∥ [11 2- 0] GaN. Analysis of TEM images shows that Au is directly in contact with Ga atoms, with no evidence of presence of Ni. The interface separation corresponds to covalent Ga and metallic Au, with a bond length of ~2.5 Å. This corresponds to an atomically abrupt transition between covalently bonded Ga and metallic bonded Au. © 2004 American Institute of Physics.