According to the present invention, a pixel TFT (an n-channel TFT) having
a considerably low OFF current value and a high ratio of an ON current value to
an OFF current value can be realized. In a pixel portion, an electrode having a
taper portion with a width of 1 m or more is formed. An impurity region
is formed by adding an impurity through the taper portion, so that the impurity
region has a concentration gradient. Then, only the taper portion is removed to
form the pixel TFT in the pixel portion. In the impurity region of the pixel TFT
in the pixel portion, the concentration gradient is provided in a concentration
distribution of the impurity imparting one conductivity, whereby a concentration
is made small on the side of a channel forming region and a concentration is made
large on the side of a semiconductor layer end portion.
