The invention provides a semiconductor and a forming method thereof, wherein the forming method of the semiconductor device comprises the following steps that a semiconductor substrate is provided, and a first interlayer dielectric layer is formed on the surface of the semiconductor substrate; a second interlayer dielectric layer is formed on the surface of the first interlayer dielectric layer; meanwhile, second interlayer dielectric layers in a first region and a second region are etched, a first groove is formed in the second interlayer dielectric layer formed in the first region, a second groove is formed in the second interlayer dielectric layer formed in the second region, in addition, the first groove comprises a first trench and a plurality of first through holes positioned at the bottom of the first trench, and a bulge is formed between the adjacent through holes; a metal blocking layer, an insulation layer and a third metal layer are sequentially formed in the first region, the metal blocking layer covers the bottom and the side wall of the first groove, and the metal blocking layer also covers the side wall and the top of the bulges. The semiconductor method and the forming method have the advantages that the mutual connection structure is formed, meanwhile, an MIM capacitor is formed, the unit area capacitance is increased, and the chip area is saved.