Abstract: A model of heat source is presented for tunnel regeneration laser diodes.Three dimension temperature distribution of the tunnel regeneration semiconductor laser with two active regions is simulated by using the finite element method,and the influence of solder voids on temperature distribution is discussed. Simulated result shows that thermal accumulating of the active region close to the substrate is higher than that of the active region close to the heat sink when there is no solder voids between the diode and the sink. Whereas localized temperature of the active region close to the heat sink rise more rapidly with localized hot spot caused by solder voids,which lead to positive feedback resulting in catastrophic optical damage (COD). The experimental phenomena are well coincident with the simulations.