Provided is a method of manufacturing a semiconductor device, the method including: forming an insulating layer on a substrate; forming a trench, which extends in a first direction parallel with the plane of the substrate, to a preset depth in the insulating layer in a second direction perpendicular to the plane of the substrate; forming a plurality of amorphous silicon strips, which extend from the inside of the trench in the second direction intersecting with the first direction, in parallel in a first direction; forming a spacer on a side of the amorphous silicon strip by using an insulating material layer; and crystallizing the amorphous silicon strip by heat treatment, wherein crystal nucleation sites are formed in the amorphous silicon layer in the trench, and a polycrystalline silicon layer is formed by lateral grain growth in a longitudinal direction of the amorphous silicon strip from the crystal nucleation site.