The effect of laminate geometry and thermal treatment on the microstructural evolution of interfacial reaction products and thin film stress in Al/SiC microlaminates has been investigated by x-ray diffraction, transmission electron and optical microscopy, and thin film stress measurements. Both stress-temperature and stress-time studies are conducted. Crystalline Si of two dimensional ‘dendritic’ morphology is observed as a solid state reaction product at the Al/SiC interface following an anneal at 400 °C. This interfacial reaction is associated with a sharp change in thin film stress in laminates with very thin AI layers to a highly compressive state during isothermal annealing at 400 °C of as-deposited laminates. The change in film stress state is in agreement with the expected larger molar volume of the likely product phases.