PURPOSE: To provide a higher barrier for the carrier having the conductivity type same as that of source and drain regions by providing a semiconductor film for channel region consisting of a plurality of layers of polycrystalline semiconductor film and giving different gain sizes to the crystal grains of mutually contact double layers of polycrystalline semiconductor films.

CONSTITUTION: A gate oxide film 13 is patterned by a polycrystalline Si film 14, a part of this polycrystalline Si film 14 on a gate electrode 12 is formed as a channel region 15 and both source region 16 and drain region 17 are formed in both sides of such channel region 15. However, the polycrystalline Si film 14 is formed by polycrystalline Si layers 14a, 14b of the double layers in place of the single layer and moreover crystal grains of polycrystalline Si films 14a, 14b are different from each other. In the case where the polycrystalline Si films 14a, 14b of the double layers in different grain sizes are mutually in contact as explained above, impurity of polycrystalline Si films 14a, 14b is precipitated on the interface of the polycrystalline Si films 14a, 14b. As a result, concentration of N-type impurity of the channel region 15 in such a location as being separated from the gate electrode 12 to the film thickness direction of the polycrystalline Si film 14 becomes high and barrier of polycrystalline Si film 14 for the P-type carrier becomes higher.