3 W cw output power has been obtained from aluminum‐free, strained‐layer double‐quantum well (DQW) InGaAs/InGaAsP/InGaP uncoated, 100‐μm‐wide stripe diode lasers (λ=0.945 μm) grown by low‐pressure MOCVD on exact (100) GaAs substrates. The combination of high‐band‐gap (1.62 eV) InGaAsP confinement layers and the DQW structure provides relatively weak temperature dependence for both the threshold current Ith as well as the external differential quantum efficiency ηd. Furthermore, the series electrical resistance for 100 μm×600 μm stripe‐contact devices is as low as 0.12 Ω. As a result, the power conversion efficiency reaches a maximum of 40% at 8×Ith, and decreases to only 33% at the maximum power (i.e., 3 W) at 28×Ith. Low‐temperature (12 K) photoluminescence measurements of InGaAs/InGaAsP quantum‐well structures exhibit narrow linewidths (<10 meV) for material grown on exact (100) GaAs substrates, while growths on misoriented substrates exhibit linewidth broadening, as a result of ‘‘step bunching.’’ Laser structures grown on misoriented substrates exhibit increased temperature sensitivity of both Ith and ηd, compared with structures grown on exact (100) substrates. © 1995 American Institute of Physics.