Microscopic voids in the die attachment solder layers of high power laser diodes (HPLDs) cause to degrade their overall thermal transfer performance. This paper presents the effects of voids on the thermal conductivity, leakage and threshold currents, characteristic temperature (T0) and output power of a single quantum well (SQW) HPLD. These effects are modeled by means of finite difference method (FDM). This numerical model calculates the time-dependent axial variations of photon density, carrier density and temperature in semiconductor laser self-consistently. The temperature dependence of the wavelength shift and the thermal mode hopping concept is also demonstrated.