Double‐heterojunction AlxGa1−xAs lasers have been prepared with a compositional discontinuity &Dgr;xat the heterojunctions of 0.45–0.68 and active region widths of ∼0.1 &mgr;m. These devices have the lowest room‐temperature threshold current densities (475 A/cm2) yet reported, with a differential quantum efficiency of 40% or more.