In laser‐assisted disordering of AlGaAs heterostructures, the Si impurity is locally incorporated with a scanned laser beam. A subsequent thermal diffusion disorders the crystal layer structure by impurity‐induced disordering. Data are presented indicating that under certain conditions the Si diffusion is anisotropic and proceeds most rapidly along the plane of the active region. The shape of the anisotropic disordering front is well suited to fabricating low‐threshold buried‐heterostructure (BH) lasers. Data describing the characteristics of the first BH lasers fabricated using the anisotropic diffusion are presented. The minimum cw threshold current is 10 mA and the maximum power output is 75 mW.