A region of an Si layer (15) located between source and drain regions (19
and 20) is an Si body region (21) which contains an n-type impurity of
high concentration. An Si layer (16) and an SiGe layer (17) are, in an as
grown state, undoped layers into which no n-type impurity is doped.
Regions of the Si layer 16 and the SiGe layer (17) located between the
source and drain regions (19 and 20) are an Si buffer region (22) and an
SiGe channel region (23), respectively, which contain the n-type impurity
of low concentration. A region of an Si film (18) located directly under a
gate insulating film (12) is an Si cap region (24) into which a p-type
impurity (5.times.10.sup.17 atoms.multidot.cm.sup.-3) is doped.
Accordingly, a semiconductor device in which an increase in threshold
voltage is suppressed can be achieved.
