A semiconductor device includes an n-type MIS transistor and a p-type MIS transistor. The n-type MIS transistor includes a first gate electrode formed on a first active region and a first sidewall formed on the side face of the first gate electrode. The p-type MIS transistor includes a second gate electrode formed on a second active region, a second sidewall formed on the side face of the second gate electrode and strain layers formed in the second active region. The second sidewall has a smaller thickness than the first sidewall.