E-beam deposited Ti/Al/Pt/Au contacts on undoped (n∼1017 cm-3) bulk ZnO showed minimum specific contact resistance, ρc, of ∼6×10-4 Ω cm2 after annealing at 250 °C. This value was essentially independent of the surface cleaning procedure employed, including sequential solvent cleaning or H2 plasma exposure. Higher annealing temperatures degraded the ρc, and Auger electron spectroscopy depth profiling revealed increasing intermixing of the metal layers. The Al outdiffuses to the surface at temperatures as low as 350 °C, and the contact metallization is almost completely intermixed by 600 °C. © 2003 American Vacuum Society.