A semiconductor device includes a transistor of a first conductivity type and a transistor of a second conductivity type. The transistor of the first conductivity type includes a first gate portion formed on a first region of a semiconductor substrate, a first sidewall formed on each side face of the first gate portion, a first protecting film formed between the first sidewall and the first gate portion, and an extension diffusion layer of the first conductivity type. The transistor of the second conductivity type includes a second gate portion formed on a second region of the semiconductor substrate, a second sidewall formed on each side face of the second gate portion, a second protecting film having an L-shaped cross-section and formed between the second sidewall and the second gate portion and between the second sidewall and the semiconductor substrate, and an extension diffusion layer of the second conductivity type.