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Surface activated bonding (SAB) method with atmospheric-pressure plasma treatment is an effective approach to develop low cost, low damage, and low temperature bonding technology. In this research, not only conventional low-pressure plasma treatment (Ar RF plasma) but also atmospheric-pressure plasma treatment (Ar+O2, Ar+H2) was investigated for low-temperature Au-Au surface-activated bonding (150degC). In the case of Au thin film to Au thin film bonding, enough bonding strength was not obtained with Ar+O2 atmospheric-pressure plasma treatment due to Au2O3 formed on Au surface. However, by using Au microbump (diameter at the top: 5 mum, height: 2 mum, and pitch: 10 mum), strong bonding strength was obtained with all these plasmas. Semiconductor laser diodes chips were successfully bonded to Si substrates wiht Au microbumps at low temperature (150degC) in ambient air using Ar+H2 atmospheric-pressure plasma treatment.