The role of Ni, An on transparent film of light emitting diodes (LEDs) has been studied by I-V and optical transmission measurement. When fixing Ni layer at 5 nm, the thickness of An layer in the Ni/Au bilayer was changed from 2 to 20 nm, the forward voltage (V-f) of LEDs decreased rapidly with increasing the thickness of Au layer. When fixing Ni layer at 10 nm, the thickness of Ni layer in the Ni/Au bilayer was changed from 2 to 20 nm, the results show that the V-f does not monotonically decrease with increasing the thickness of Ni layer. It is found that Au layer play a role of spreading the injection current while the Ni layer play a role of reducing the Schottky barrier height. The effect of thermal treatment on the behavior of the ohmic contact of Ni/Au to p-GaN contacts was also investigated by I-V measurement. It is found that it exists a reversible process of contact resistance when the Ni/Au to p-type GaN contacts is annealed in air and N-2 ambient alternatively. (C) 2003 Elsevier Ltd. All rights reserved.