A first shape of semiconductor region having on its one side a plurality of sharp convex top-end portions is formed first and a continuous wave laser beam is used for radiation from the above region so as to crystallize the first shape of semiconductor region. A continuous wave laser beam condensed in one or plural lines is used for the laser beam. The first shape of semiconductor region is etched to form a second shape of semiconductor region in which a channel forming region and a source and drain region are formed. The second shape of semiconductor region is disposed so that a channel forming range would be formed on respective crystal regions extending from the plurality of convex end portions. A semiconductor region adjacent to the channel forming region is eliminated.