The invention discloses a preparation method of a fin-like structure. The method comprises the following steps: providing a substrate, and forming a plurality of fins on the substrate; depositing shallow slot isolation among the plurality of fins; performing first planarization treatment and first corrosion treatment on the shallow slot isolation in sequence; performing second corrosion treatmenton the plurality of fins; filling a material layer on the formed structure, and performing an etchback treatment on the material layer; removing residues on the top of the shallow slot isolation at ahigh selection ratio, and removing the material layer in a second corrosion treatment area; epitaxially growing a high migration rate material in the second corrosion treatment area to form an importing structure; performing second planarization treatment on the importing structure; and performing third corrosion treatment on the shallow slot isolation to form the fin-like structure. According tothe preparation method of the fin-like structure, no corresponding "grain defect" is formed during the epitaxial growth of the high migration rate material, and no influence is generated on the efficiency or quality of the epitaxial growth. The invention further provides a preparation method of a semiconductor device.