The temperature characteristics of 1.3 &mgr;m InGaAsP/InP buried heterojunction lasers are investigated using a fully self‐consistent two dimensional numerical model. Devices operating at 1.3 &mgr;m are very temperature sensitive and therefore the model includes for the first time coupled solutions to the thermal as well as the electrical and optical equation sets. Good agreement is found with experimental results, including the temperature dependence of the threshold current and the prediction of a break‐point temperature.