High efficiency, low threshold visible AlGaInP/GaInP laser diodes using a buried AlAs native oxide for carrier and optical confinement are described. The lasers incorporate a thin AlAs layer in the upper cladding region, which when laterally wet oxidized, forms a narrow aperture. The lasers exhibited modest performance under continuous wave (cw) operation. Low temperature (400 °C) post-fabrication annealing was shown to dramatically improve the device characteristics. The lasers operate with room temperature cw threshold currents of 20 mA with external differential quantum efficiencies of 27&percent; per facet (0.25 W/A per facet) for an uncoated 625-&mgr;m-long, 3.5-&mgr;m-wide device. ©1997 American Institute of Physics.