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Crack formation mechanism in laser-welded Aucoated Invar materials for semiconductor laser packaging is investigated experimentally and numerically. Experimental results obtained from metallography, scanning electron microscope (SEM), SEM mapping, and energy dispersive spectrometer (EDS) line profile show that high concentration of Au composition accumulate near the crack region. The cause of Au accumulation may come from the segregation of Au along the crack region. A finite-element method (FEM) is performed on the calculation of thermal stresses during spot-welding for Au-coated Invar materials. Numerical results show that the high tensile stresses of the Au segregation layer generated by rapid solidification shrinkage is the possible cause for crack formation. Both experimental and numerical results suggest that the crack formation mechanism in laser-welded Au-coated optoelectronic materials is directly related to the combined effects of the Au segregation and high tensile stresses induced by the strain shrinkage during the final stage of solidification.Index Terms-Finite-element method, laser welding, optoelectronic packaging, segregation.