We report the growth of ultra-thin indium oxide layers using the dc-magnetron sputtering method. We demonstrate that good quality tunnel barriers made of indium oxide can be routinely fabricated and employed in spintronic-related devices. Simple magnetic tunnel junctions (MTJs) were fabricated in a cross geometry using ex situ thermally evaporated cobalt and permalloy. Our best junctions obey the Rowell criteria for tunneling and exhibit a tunnel magnetoresistance of 15% at 100 K. (C) 2004 Elsevier B.V. All rights reserved.