AlGaInP-based, high power laser diodes operating at wavelengths of 630 to 645 nm have been designed, fabricated, and characterized. Cw output powers approaching 1 Watt and thresholds below 400 A/cm2 have been achieved. Measurement of internal laser parameters indicates low internal loss and transparency current, high gain, and moderate internal quantum efficiency. Characteristic temperature data suggest that the lowest practical operating wavelength of similar diodes is close to 620 nm. Examination of performance as a function of cavity length indicates an optimum length in the range of 1200 micrometers .