High-power GaAlAs lasers using the large optical cavity buried-heterostructure (LOC-BH) window structure, which provides transverse index guiding in the nonabsorbing facet region, have been fabricated. Threshold currents between 30 and 50 mA and differential quantum efficiencies of 0.85 mW/ mA have been measured. CW and pulsed output powers up to 88 and 372 mW, respectively, have been attained.