Method to manufacture semi-conductor device

The invention discloses a method to manufacture a semi-conductor device. The method includes that a) providing a semi-conductor substrate where a first dummy gate used for forming an N-type metal gate and a second dummy gate used for forming a P-type metal gate are formed and where an interlayer dielectric layer surrounding the first dummy gate and the second dummy gate is formed; b) removing one of the first dummy gate and the second dummy gate to form a first filling opening and to form a first metal gate in the first filling opening; c) forming a protection layer on the first metal gate; d) removing the left one of the first dummy gate and second dummy gate to form a second filling opening; and e) forming a second metal gate in the second filling opening to remove the protection layer. According to the method, the protection layer is formed on the surface of the firstly formed metal gate to protect the metal gate from being damaged in the later etching process and the cleaning process, and accordingly failure of the semi-conductor device can be effectively avoided.