A simple form of a buried heterostructure AlxGa1−xAs‐GaAs quantum‐well laser is described that is realized by impurity‐induced layer disordering (donor‐induceddisordering). The layer disordering [and the resulting band‐gap shift to higher energy (and lower index)] is accomplished by Si diffusion in a stripe pattern defined by a Si3N4mask. Single‐mode lasers of stripe width 3 and 6 &mgr;m are demonstrated that operate continuously at 300 K in the threshold current range of 10–25 mA and with single‐facet power levels as high as 10–20 mW.