A semiconductor device having high operating performance and reliability, and a manufacturing method thereof are provided.
An LDD region
provided in an n-channel TFT
forming a driving circuit enhances the tolerance for hot carrier injection. LDD regions
provided in an n-channel TFT (pixel TFT)
forming a pixel portion greatly contribute to the decrease in the OFF current value. Here, the LDD region of the n-channel TFT of the driving circuit is formed such that the concentration of the n-type impurity element becomes higher as the distance from an adjoining drain region decreases.