Patent ID: 7355214

Claim:
A semiconductor device comprising: a p-channel type field effect transistor and an n-channel type field effect transistor both formed in a semiconductor layer which has a strain effect and which is formed in an upper layer of a semiconductor substrate, wherein a source/a drain of said p-channel type field effect transistor and a source/a drain of said n-channel type field effect transistor are formed only in said semiconductor layer having the strain effect, wherein said semiconductor layer having the strain effect comprises a silicon layer having a strain effect, and wherein said semiconductor substrate comprises: a silicon base; a buffer layer formed on said silicon base, said buffer layer being made from silicon germanium in which the concentration of germanium is changed in the thickness direction; a relax layer formed on said buffer layer, said relax layer being made from silicon germanium whose stress is relaxed; and a silicon layer formed on said relax layer, said silicon layer having a strain effect.