We report the first successful use, to our knowledge, of InAsP quantum wells for 1.55 mu m wavelength laser emission: 5 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. Strain relaxation issues do not severely limit the multi-quantum-well design since up to 17 quantum wells were integrated in a strain-balanced laser which showed equally good characteristics.