Data are presented demonstrating the continuous (cw) room‐temperature (23 °C) operation of planar index‐guided ‘‘buried‐mesa’’ AlxGa1−xAs‐In0.5(AlyGa1−y)0.5P‐ In0.5Ga0.5P heterostructure visible‐spectrum laser diodes. The planar ‘‘mesa’’ structure is formed by ‘‘wet’’ oxidation (H2O vapor+N2carrier gas, 550 °C) of the AlxGa1−xAs on the composite AlxGa1−xAs‐In0.5(AlyGa1−y)0.5P upper confining layer (outside of the active stripes). The oxidation process results in a ∼0.5‐&mgr;m‐thick native oxide located (in depth) within ∼3000 A˚ of the active layer in the region outside of the laser stripes themselves. The oxide possesses excellent current‐confinement properties and a low refractive index (n≊1.60), resulting in relatively low‐threshold laser operation for narrow‐stripe devices. In addition, these devices exhibit transverse‐mode confinement and small beam astigmatism because of the refractive index step provided by the deep native oxide.