Abstract: A semiconductor device includes, a gate insulating film, a gate electrode, a source/drain region, and a Si mixed crystal layer in the source/drain region. The Si mixed crystal layer includes a first Si mixed crystal layer that includes impurities with a first concentration, a second Si mixed crystal layer formed over the first Si mixed crystal layer and that includes the impurities with a second concentration higher than the first concentration, and a third Si mixed crystal layer formed over the second Si mixed crystal layer and that includes the impurities with a third concentration lower than the second concentration.