A semiconductor device and fabrication thereof is disclosed in which devices are formed on two devices regions of opposite conductivity types by selectively masking and implanting the same type of dopant into active regions of both device regions. The process includes masking part of the active regions in each device region and implanting a dopant into exposed active regions in both devices regions. The number of masking, implantation and other steps required in the fabrication process are reduced by the selective masking of various active regions. Non-symmetrically doped source and drain regions may be formed on the transistors among a group which lie closest to the opposite device region.