We report on a study of lasers with an emission wavelength of about 1.5 μm and high temperature stability, synthesized on an InP (001) substrate. Self-organized InAs quantum dots capped with a thin GaAs layer are used as the active region of the laser. A quaternary InGaAsP solid solution with a band-gap width of 1.15 eV serves as the waveguide/matrix layer. A high characteristic temperature of the threshold current, T0 = 205 K, is reached in the temperature range 20–50°C in ridge-waveguide laser diodes. A correlation between the values of T0 and the band-gap width of the waveguide layers is found.