A method of forming a semiconductor device is disclosed. A substrate having a first device region and a second device region is provided. A metal nitride barrier layer is formed to cover the first device region and the second device region. A titanium layer is deposited on the metal nitride barrier layer. The titanium layer is selectively removed from the second device region, thereby exposing the metal nitride barrier layer in the second device region. The titanium layer in the first device region is transformed into a titanium nitride layer. The titanium nitride layer is a work function layer on the first device region.