We report on the zinc oxide doped indium oxide (ZIO) transparent ohmic contact to the p-GaN. Optimum conditions were selected to minimize the lowest specific contact resistance to 1.4 x 10(-4) Omega cm(2), as examined by transmission line model after heat treatment process at an alloying temperature of 500 S C for 10 min in air. ZIO films were also applied to GaN-based light-emitting diodes (LEDs) to form an electrode with a p-type ohmic contact. A light output power and an external quantum efficiency of the LED with ZIO contact of 5.61 mW and 10.63%, respectively, were measured at a forward current of 20 mA at room temperature. (c) 2006 The Electrochemical Society.