A TFT of the present invention includes a gate electrode, a gate insulating film and a first semiconductor film which are sequentially formed on an insulating substrate, a second semiconductor film including a high density impurity which is formed on the first semiconductor film while being separated into portions at grade and a first electrode and a second electrode, each of which is formed on the separated second semiconductor film. Further, a peripheral portion of the first semiconductor film includes a protruded portion toward the outside from an edge of the second semiconductor film, and a surface of the protruded portion is roughened. By roughening the surface of the protruded portion, an on-current of the TFT can be maintained and the leakage current can be suppressed.