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 (150°C). 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 Au 2O3 formed on Au surface. However, by using Au microbump (diameter at the top: 5 μm, height: 2 μm, and pitch: 10 μm), 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 (150°C) in ambient air using Ar+H2 atmospheric-pressure plasma treatment.