The contact characteristics on bulk single-crystal n-type ZnO of an Ir/Au metallization scheme deposited by sputtering are reported as a function of annealing temperature in the range 200 - 1000 degrees C (N-2 ambient). The contacts exhibited ohmic behavior for all temperatures and show a minimum specific contact resistivity of 3.6 x 10(-5) Omega cm(2) after a 1000 degrees C anneal. The contacts transition to rectifying behavior after annealing above 1100 degrees C, coincident with a degraded surface morphology including agglomeration of Ir to the surface and heavy intermixing of the Ir and Au. The Ir contacts exhibit higher thermal stability but poorer specific contact resistivity than conventional Ti/Au metal stacks on bulk n-type ZnO. The contacts showed very little change in resistance after extended aging (30 days) at 350 degrees C. Annealing under O-2 ambient led to an increase in contact resistivity by orders of magnitude. (c) 2007 The Electrochemical Society.