The thermal and the optoelectronic performance of high power gallium arsenide (GaAs) laser diode die-attached with sintered silver joint were investigated. The thermal and mechanical characteristics of the Laser bar packaging were simulated by finite element analysis (FEA). On the basis of prior experimental observations, voids in the bonding layer were intentionally introduced in the FEA model to examine their effect on the laser diode operating in the continuous-wave (CW) mode under different drive currents. The simulation results indicate that the quality of the bonding layer is very important to the heat dissipation capability of the packaging. Any void in the die-attach material would become a hotspot and thus deteriorate the optoelectronic performance of the laser diode. In addition, because of the coefficient of thermal expansion (CTE) mismatch between the laser bar and the copper heat sink, the interfacial thermomechanical stress will cause a noticeable curvature of the laser diode and a blueshift in the wavelength.