A model of internal heat source distribution is presented for quantum-well laser. Three-dimensional temperature distribution of the stripe quantum-well laser is simulated by using the finite element method, and the influence of solder voids between chip and heat sink on the steady-state temperature distribution is discussed. It is found that the chip′s internal temperature distribution is influenced by the position and size of solder voids. The localized hot spot may result from the nether solder voids, and the strong localized temperature rises and the hot spot expands with the expanding of the void′s dimension. Simulated result shows further that the strongest temperature rise is caused by solder voids under the center of the electrode stripe, and moreover, the highest temperature lies at the front facet. So catastrophic optical damage (COD)will be found at the front facet most possibly, which is in agreement with the test.