By using chemical beam epitaxy at growth temperatures as low as 460–480 °C, we have overcome strain relaxation problems that prevented so far the successful use of InAsP quantum wells in 1.55 &mgr;m lasers. Five quantum well InAsP/InGaAsP horizontal cavity lasers showed 88&percent; internal efficiency,1.6 cm−1losses per well, and33 A/cm2transparency current density per well, which equal or even surpass the best published characteristics for 1.55 &mgr;m wavelength lasers based on any material system. Moreover, up to 17 quantum wells were integrated in a strain-balanced laser, which showed equally good characteristics. ©1997 American Institute of Physics.