There is a strong interest in developing thermally stable metallization schemes for ZnO and boride-based contact stacks are expected to have potential because of their thermodynamic stability. The contact characteristics on bulk single-crystal n-ZnO of a ZrB2/Pt/Au metallization scheme deposited by sputtering are reported as a function of annealing temperature in the range 300-800 degrees C. The contacts were rectifying for anneal temperatures < 500 degrees C but exhibited Ohmic behavior at higher temperatures and exhibit a minimum specific contact resistivity of 9 x 10(-3) ohm CM after 700 degrees C anneals. The contact stack reverts to rectifying behavior after annealing above 800 degrees C, coincident with a degraded surface morphology and intermixing of the Au, Pt and ZrB2. The boride-based contacts exhibit higher thermal stability but poorer specific contact resistivity than conventional Ti/Au metal stacks on ZnO. (c) 2006 Elsevier B.V. All rights reserved.