According to one embodiment, a method of manufacturing a semiconductor device including forming a first SiGe layer on an insulating film, processing the first SiGe layer to have an island shape which includes a first region and a second region, the first region having a width larger than a width of the second region in a direction perpendicular to a connecting direction of the second region, subjecting the first SiGe layer having the island shape to thermal oxidation, thereby increasing Ge composition of the first and second region, and setting the Ge composition of the second region to be higher than the Ge composition of the first region, melting the second region having the increased Ge composition by heat treatment, and recrystallizing the melted second region from an interface between the first and second region.