A MOS transistor including a substrate, a gate dielectric layer on the substrate, a stacked gate on the gate dielectric layer, and a source/drain in the substrate beside the stacked gate is provided. In particular, the stacked gate includes, from bottom to top, a first barrier layer, an interlayer, a work-function-dominating layer, a second barrier layer and a poly-Si layer, wherein the work-function-dominating layer includes a metallic material.