In a method of manufacturing a semiconductor device, a fin structure is formed over a substrate. The fin structure is sculpted to have a plurality of non-etched portions and a plurality of etched portions having a narrower width than the plurality of non-etched portions. The sculpted fin structure is oxidized so that a plurality of nanowires are formed in the plurality of non-etched portions, respectively, and the plurality of etched portions are oxidized to form oxides. The plurality of nanowires are released by removing the oxides.