A device includes a substrate, a semiconductor fin over the substrate, and a gate dielectric layer on a top surface and sidewalls of the semiconductor fin. A gate electrode is spaced apart from the semiconductor fin by the gate dielectric layer. The gate electrode includes a top portion over and aligned to the semiconductor fin, and a sidewall portion on a sidewall portion of the dielectric layer. The top portion of the gate electrode has a first work function, and the sidewall portion of the gate electrode has a second work function different from the first work function.