Investigations on InGaAs/InGaAsP multiquantum well separate-confinement lasers emitting in the 1.3 μm wavelength range requiring extremely thin wells of the order of 2 nm are presented. Multiquantum well laser structures with varying numbers of wells and different thicknesses of the barrier layers were grown using low-pressure MOVPE, and were intensively characterised in terms of the threshold current performance and temperature behaviour. Structures comprising 10–15 nm thick barriers and up to 12 wells gave threshold current densities for infinite cavity lengths in the range of 780–1030 A/cm2, being somewhat smaller than those values measured on comparable 1.3 μm bulk lasers. On the other hand, lasers with both smaller and larger barrier thicknesses as well as higher numbers of wells showed greatly increased threshold current densities which may be attributed to higher internal losses and inhomogeneous carrier injection, respectively. Independent of the number of wells and of the thickness of the barriers, all samples under investigation exhibited a characteristic temperatureT0, of about 60 K in the temperature range 5–50°C.