a semiconductor device , specifically a complementary metal oxide semiconductor device , has a substrate on which are formed first and second field effect transistors . each of the field effect transistors comprises a source - drain region , a channel of either an n - type or a p - type conductivity semiconductor material formed on the substrate , a first gate region , and a first dielectric region that separates the first channel from the first gate region . however , dissimilar semiconductor materials are used to form the channel regions of the first and second field effect transistors so that high electron and hole mobility can be achieved .