Specific contact resistances between an amorphous oxide semiconductor, In-Ga-Zn-O, and various metallic electrodes, Ag, Au, In, Pt, Ti, polycrystalline indium tin oxide (ITO) and amorphous indium zinc oxide (a-IZO), were examined. All the contacts except for An and Pt showed linear current-voltage characteristics, while Au and Pt did Schottky contacts. Low contact resistances < 10(-4) Omega cm(2) were obtained for the Ag, In, Ti, ITO and a-IZO contacts, and there is a trend that the contact resistance decreases with decreasing the work function of the metallic electrode. The performances of thin film transistors using ITO and Ti for source and drain contacts were better than that using the Schottky Au contacts. It was also found that the Ti contacts have a large distribution in the contact resistance, suggesting that a higher reproducibility process should be employed when reactive metals are used for an electrical contact to an oxide semiconductor. (C) 2007 Published by Elsevier B.V.