A semiconductor device structure is provided. The semiconductor device structure includes a substrate having a doped region in an upper portion of the substrate. The doped region is doped with first dopants of a first conduction type. The semiconductor device structure includes one fin structure over the substrate. A first dopant concentration of the doped region exposed by the fin structure is greater than a second dopant concentration of the doped region covered by the fin structure. The semiconductor device structure includes an isolation layer over the substrate and at two opposite sides of the fin structure. The semiconductor device structure includes a gate over the isolation layer and the fin structure.