The morphology of a Ni(5nm), Au(45nm), Ge(20nm) ohmic contact with a ZrB2 (50nm) diffusion barrier, annealed to temperatures between 355°C and 485°C, was studied by TEM. The barrier was found to remain intact and unreacted after annealing. The contact annealed to 355°C reacted in the solid state to form αAu-Ga, Ge and orthorhombic NiGe phases. The morphology of contacts annealed above the melting point (∼ 380°C) consisted of two regions; type A contained αAu-Ca and NiGeAs, and type B contained αAu-Ga α′Au-Ga, NiGe and epitaxial Ge. αAu-Ga segregated to the contact pad edges at and above 403°C. The transition from rectifying to ohmic properties corresponded to annealing above the melting point of the contact. It was found that variations in contact resistance with temperature could be explained either by changes in the bulk or in the edge morphology.