Semiconductor structure and forming method thereof

The invention discloses a semiconductor structure and a forming method thereof, and the method comprises the steps: providing a substrate which comprises an isolation region, a first device region and a second device region; a plurality of first fin parts arranged in the second direction are formed on the substrate, isolation openings are formed in the first fin parts, and the isolation openings are located in the first region; a dielectric layer and a plurality of precursor structures are formed on the substrate, the precursor structures stretch across the first fin parts in the second direction, and the dielectric layer covers the side walls of the precursor structures; and performing oxidation treatment on the precursor structure located on the first region and adjacent to the isolation opening to form a first isolation structure. The first isolation structure is directly formed by oxidizing the precursor structure, and the removal process of the gate structure does not need to be carried out, so that the