100 nm thick Ru films were deposited onto n-ZnO epitaxial layers by radio frequency sputtering. It was found that highly transparent RuOx was formed after O-2 annealing. With an incident wavelength of 460 nm, it was found that transmittances of as-grown, 500 degrees C- annealed, 600 degrees C- annealed, and 700 degrees C-annealed Ru films were 56.8, 73.5, 79.6, and 86.8%, respectively. It was also found that as-deposited Ru formed Schottky contact on n-ZnO. However, good ohmic contacts were formed between the annealed Ru films and the underneath ZnO. With 650 degrees C annealing, we achieved a specific contact resistance of only 2.72 X 10(-4) Omega cm(2). Such a low specific contact resistance should be attributed to the formation of RuOx and the dissociation of oxygen atoms in ZnO during annealing. (c) 2006 The Electrochemical Society.