The barrier effect of Pt and Ni has been investigated in the Ti/Al/Pt/Au and Ti/Al/Ni/Au Ohmic contacts to n-GaN, respectively. Severe indiffusion of Pt and An has been found in the 800 degrees C annealed Au/Pt/Al/Ti/n-GaN samples. However, Ni does not penetrate into the n-GaN and shows better barrier effect for preventing An penetration into Au/Ni/Al/Ti/n-GaN samples. The reaction between Ga and Pt has also been identified in the samples annealed at 600 degrees C. At the same time, the electrical degradation was found for the Ti/Al/Pt/Au samples aged at 600 degrees C. However, no obvious degradation was found for the aged Ti/Al/Ni/Au samples. It is suggested that the reaction between Ga. and Pt may cause the electrical degradation of the Ti/Al/Pt/Au metallization system. (c) 2006 Elsevier B.V. All rights reserved.