We demonstrate a very high-power AlGaAs single quantum well GRINSCH ridge laser operating in a diffraction-limited fundamental transverse mode up to 360 mW at a wavelength of 856 nm. the maximum power output of the laser reached 425 mW and was limited by thermal saturation of the device and not by catastrophic optical mirror damage. These lasers not only exhibit very high power levels, but also show excellent reliability at high output power levels. the extremely high, CW fundamental mode power combined with very low-intensity and optical low-phase distortion as well as low astigmatism render this ridge waveguide laser very suitable for optical storage systems, printers, and direct frequency doubling. These devices have been successfully used for direct frequency doubling of their output in a resonant KNb03 cavity yielding 41 mW of blue radiation at 428 nm. © 1991 IEEE.