Ridge waveguide lasers at 1.5 μm wavelength have been fabricated by liquid-phase epitaxy with CW thresholds of 18 mA at 20°C, single transverse mode operation to 25 mW and quantum efficiencies over 20% per facet. Thresholds have increased by less than 2 mA in 10000 h for devices maintained at 5 mW output and 50°C. Packaged devices with single-mode fibre tails have shown excellent performance in systems trials at 2.4 Gbit/s.