In a semiconductor film having a heterojunction structure, for example a semiconductor film (11) including a SiGe layer (2) and a Si layer (3) formed on the SiGe layer (2), impurity concentration is controlled in such a manner that the concentration of impurity in the lower, SiGe layer (2) becomes higher than that in the upper, Si layer (3) by exploiting the fact that there is a difference between the SiGe layer (2) and the Si layer (3) in the diffusion coefficient of the impurity. The impurity contained in the semiconductor film 11 is of the conductivity type opposite to that of the transistor (p-type in the case of an n-type MOS transistor whereas n-type in the case of a p-type MOS transistor). In this way, the mobility in a semiconductor device including a semiconductor film having a heterojunction structure with a compression strain structure is increased, thereby improving the transistor characteristics and reliability of the device.