A method of integrated circuit (IC) fabrication includes exposing a plurality of channel regions including a p-type channel region and an n-type channel region; forming a gate dielectric layer over the exposed channel regions; and forming a work function metal (WFM) structure over the gate dielectric layer. The WFM structure includes a p-type WFM portion formed over the p-type channel region and an n-type WFM portion formed over the n-type channel region, and the p-type WFM portion is thinner than the n-type WFM portion. The method further includes forming a fill metal layer over the WFM structure such that the fill metal layer is in direct contact with both the p-type and n-type WFM portions.