High quality platinum Ohmic contacts on unintentionally doped n-type ZnO epitaxial layers grown by pulsed laser deposition on (0 0 0 1) sapphire substrates, are reported. The contacts were formed by using a Ga focused ion beam and Pt direct-write metal deposition. Contact resistance measurements by the transmission line method, produced values as low as 3 x 10(-4) Omega cm(2) without any annealing. An optimum Ga surface-modification dosage window is determined, within which the current transport mechanism of these contacts was found to proceed mainly by tunneling through the Ga-ZnO interface layer. (C) 2002 Elsevier Science Ltd. All rights reserved.