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 .mu.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.