Room-temperature c.w. operation has been achieved for stripe-geometry double heterostructure InP/InGaAsP/InP diode lasers emitting at 1.55 µm. The heterostructures were grown by l.p.e. on (100) InP substrates, and stripes were defined by the conventional planar-stripe structure. The room-temperature (20°C) c.w. threshold current was ≃ 250 mA for a 6 µm wide by 200 µm long cavity. © 1979, The Institution of Electrical Engineers. All rights reserved.