A semiconductor structure and a manufacturing method thereof are provided. The semiconductor structure includes a substrate, a first dielectric layer, a first doping layer of a first conductivity type, and a second doping layer of a second conductivity type. The substrate has a fin portion. The first dielectric layer is disposed on the substrate and surrounds the fin portion. The first doping layer of the first conductivity type is disposed on the first dielectric layer and is located on two opposite sidewalls of the fin portion. The second doping layer of the second conductivity type is disposed on the two opposite sidewalls of the fin portion and is located between the fin portion and the first doping layer. The first doping layer covers a sidewall and a bottom surface of the second doping layer.