A method of fabricating a metal gate transistor includes providing a substrate. An interlayer dielectric layer covers the substrate. A dummy gate is embedded in the interlayer dielectric layer. A high-k dielectric layer is disposed between the dummy gate and the substrate. Later, the dummy gate is removed to form a trench, and the high-k dielectric layer is exposed through the trench. After the dummy gate is removed, an ion implantation process is performed to implant fluoride ions into the high-k dielectric layer. Finally, after the ion implantation process, a metal gate is formed to fill in the trench.