A high-power laser in the 780 nm wavelength region has been realized by introducing an AlGaAs ternary alloy quantum-well structure. Investigations focus on the characteristic temperature and catastrophic optical damage (COD) level. It is found that a triple quantum-well (TQW) active layer structure has superior characteristics for high-power operation. Stable operation for over 1000 h under 50-degrees-C and 60 mW conditions is achieved. A relatively high characteristic temperature of around 150 K is also obtained.