The invention discloses a
semiconductor structure and a forming method thereof. The forming method comprises the steps of providing a substrate, a gate structure, a side wall located on the side wall of the gate structure, a source-drain doped region, a bottom
dielectric layer and a source-drain
contact layer; removing the side wall to form a gap; forming a protective layer covering the bottom and the side wall of the gap in a shape-preserving manner; and forming a top
dielectric layer on the bottom
dielectric layer, wherein the top
dielectric layer seals the gap to form an air gap. According to the embodiment of the invention, after the substrate is provided, the side walls are removed to form the gap, the bottom and the side walls of the gap are covered with the protective layer in a shape-preserving manner, and then the top
dielectric layer for sealing the gap is formed, so that the air gap and the protective layer are correspondingly of an integrated structure, and the protection effect of the protective layer on the bottom and the side walls of the gap is improved; the damage probability of the film layer structures (such as the gate structure and the substrate) at the bottom and the side wall of the gap is reduced, the integrity of the film layer structures at the bottom and the side wall of the gap is correspondingly improved, and then the reliability and the production yield of the
semiconductor structure are improved.