By using chemical beam epitaxy at growth temperatures as low as 460-480 degrees C, we have overcome strain relaxation problems that prevented so far the successful use of InAsP quantum wells in 1.55 mu m lasers. Five quantum well InAsP/InGaAsP horizontal cavity lasers showed 88% internal efficiency, 1.6 cm(-1) losses per well, and 33 A/cm(2) transparency current density per well, which equal or even surpass the best published characteristics for 1.55 mu 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. (C) 1997 American Institute of Physics.