The thermal characteristics and CW operation of buried-heterostructure (BH) injection lasers, in which the GaAs active regions are completely buried in Ga1-xAlxAs, are described. The narrow active regions of these diodes facilitate effective heat dissipation. Thus, the CW operation of these lasers has been achieved without the p-GaAs layers usually grown in double-heterostructure (DH) lasers for electrical contacting purposes and with the heat dissipation through n-GaAs substrates. Even in this disadvantageous configuration, the temperature rise in the active regions of BH lasers at threshold is much smaller than that of p-side-down DH lasers. The calculation using an approximate formula can explain these low experimental values fairly well. Due to low operating current and effective heat dissipation, BH lasers can be operated continuously at room temperature on very small heat sinks such as TO-5 transistor headers.