A semiconductor device having high operating performance and reliability is disclosed, and its fabrication process is also disclosed.In an n-channel type TFT 302, an Lov region 207 is disposed, whereby a TFT structure highly resistant to hot carriers is realized. Further, in an n-channel type TFT 304 forming a pixel portion, Loff regions 217 to 220 are disposed, whereby a TFT structure having a low OFF-current value is realized. In this case, in the Lov region, the n-type impurity element exists at a concentration higher than that of the Loff regions, and the whole of the n-type impurity region (b) which constitutes the Lov region is sufficiently activated by optical annealing, so that a good junction portion is formed between the n-type impurity region and the channel forming region.