A semiconductor structure and its fabrication method are provided in the present disclosure. The method includes providing a base substrate, forming a plurality of discrete core layers on the base substrate, forming an isolation layer on a top surface of a core layer, forming a sacrificial layer on the base substrate and exposing a top surface of the isolation layer, removing the isolation layer after forming the sacrificial layer, removing the sacrificial layer after removing the isolation layer, forming a mask layer on a sidewall surface of the core layer after removing the sacrificial layer, and removing the core layer after forming the mask layer.