Manufacture of TFTs corresponding to various circuits makes structures thereof complex, which involves a larger number of manufacturing steps. Such an increase in the number of the manufacturing steps leads to a higher manufacturing cost and a lower manufacturing yield. In the invention, a high concentration of impurities is doped by using as masks a tapered resist that is used for the manufacture of a tapered gate electrode, and the tapered gate electrode, and then the tapered gate electrode is etched in the perpendicular direction using the resist as a mask. A semiconductor layer under the thusly removed tapered portion of the gate electrode is doped with a low concentration of impurities.