The invention provides a forming method of a
semiconductor structure and a forming method of a
transistor. The forming method of the
semiconductor structure comprises the steps that a
semiconductor substrate is provided, the semiconductor substrate is made of an insulator upper semiconductor comprising a substrate, an
insulation layer and a semiconductor layer; a
hard mask layer is formed on the surface of the semiconductor substrate; part of the
hard mask layer is removed, the rest of the
hard mask layer serves as masks, forms a plurality of openings inside the semiconductor layer, and the surface of the
insulation layer is exposed out; the side walls of the openings are etched by adopting the
crystal orientation anisotropism wet process, and double-layer discrete nanowires are formed; then, the rest of the hard
mask layer is removed, the
insulation layer between the nanowires and the substrate is removed, and the double-layer discrete nanowires are suspended above the substrate; after the rest of the hard
mask layer and the insulation layer are removed, thermal annealing is conducted on the nanowires so that the cross section of each
nanowire becomes round. The forming method of the
semiconductor structure is low in production cost, simple in process, and suitable for large-scale production.