Interfacial reactions between thin films of Al and amorphous (a‐) SiC annealed with tungsten‐halogen lamps lead to the formation of Si fractal‐like structures at temperatures as low as 275 °C in less than 100 s. By usinga‐SiC/Al/a‐SiC sandwiches with different SiC/Al thickness ratios, it is shown that the nucleation of Si crystals is faster on smaller‐grained Al. This is attributed to the higher Al surface energy and the increased density of high‐energy multiple grain junctions in thinner (smaller grained) Al layers. When the Al layer is very thin (≤50 A˚) a solid‐state amorphization reaction occurs between Al anda‐SiC without subsequent Si crystallization. Formation of Al4C3follows Si crystallization, or in the very thin Al layer, the amorphization reaction.