Process conditions for fabricating Si‐O impurity‐induced layer disorder defined AlxGa1−xAs‐GaAs buried heterostructure quantum well lasers utilizing a fully self‐aligned planar process and conventional As free open‐tube‐furnace annealing are presented. An SiO2layer, deposited by sputtering, was used as a diffusion source for Si and O impurities as well as a source for Ga vacancies that enhance impurity diffusion and allow for a reduction in the required annealing temperature and time. A self‐aligned native oxide of the AlxGa1−xAs cladding layer was used to form a Zn diffusion mask and dielectric layer. Lasers fabricated using this process exhibited threshold currents as low as 2.72 mA and external differential quantum efficiencies of 79% at room temperature in continuous operation.