In a method of manufacturing a semiconductor device, a gate structure is formed over a fin structure. A source/drain region of the fin structure is recessed. A first semiconductor layer is formed over the recessed source/drain region. A second semiconductor layer is formed over the first semiconductor layer. The fin structure is made of SixGe1-x, where 0≤x≤0.3, the first semiconductor layer is made of SiyGe1-y, where 0.45≤y≤1.0, and the second semiconductor layer is made of SizGe1-z, where 0≤z≤0.3.