The present invention relates to complementary metal-oxide-semiconductor (CMOS) circuits that each contains at least a first and a second gate stacks. The first gate stack is located over a first device region (e.g., an n-FET device region) in a semiconductor substrate and comprises at least, from bottom to top, a gate dielectric layer, a metallic gate conductor, and a silicon-containing gate conductor. The second gate stack is located over a second device region (e.g., a p-FET device region) in the semiconductor substrate and comprises at least, from bottom to top, a gate dielectric layer and a silicon-containing gate conductor. The first and second gate stacks can be formed over the semiconductor substrate in an integrated manner by various methods of the present invention.