Semiconductor structure

A semiconductor structure including a silicon substrate, a nucleation layer and a plurality of multi-layer sets is provided. The nucleation layer is disposed on the silicon substrate. The multi-layer sets are stacked over the nucleation layer, and each of the multi-layer sets includes a plurality of first sub-layers and a plurality of second sub-layers stacked alternately. A material of the first sub-layers and the second sub-layers includes Al-containing III-V group compound, wherein an average content of aluminum of the multi-layer sets decreases as a minimum distance between each of the multi-layer sets and the silicon substrate increases, and an aluminum content of the first sub-layers is different from an aluminum content of the second sub-layers.