The thermal stabilities of Ti/Pt/Au, W/Au and Cu bonding layers on GaN blue laser diode were investigated by measuring the series resistances with respect to annealing temperatures from 250 degrees C to 500 degrees C and possible degradation mechanisms were suggested by Transmission Electron Microscopy and Energy Dispersive Spectroscopy analyses. The laser diode with Ti/Pt/Au bonding layer degraded after annealing at 250 degrees C but the laser diode with Cu and W/Au bonding layer showed good thermal stability up to 400 degrees C and 450 degrees C, respectively. Cu and W/Au layers are believed to improve the integrities of the ohmic contact and bonding layers and this would enhance the thermal stability of bonding layers. Therefore robust GaN blue laser diodes that have wide operation windows and long-term reliability would be obtained. (c) 2007 Elsevier B.V. All rights reserved.