Leaky‐mode buried‐heterostructure injection lasers are fabricated and operated successfully under pulse bias at room temperature. The lasers consist of a thin active layer confined by paralleln‐ andp‐AlxGa1−xAs layers with a high mole fraction of AlAs (x=0.4) and perpendicularp−‐AlyGa1−yAs layers with a low mole fraction of AlAs (y=0.25). It is shown that most of the laser power can be coupled out into the low‐loss perpendicular layers and emitted from the end facets, resulting in highly collimated beams with a beam divergence of about 1°.