A manufacturing method for semiconductor device having metal gate includes providing a substrate having a first semiconductor device and a second semiconductor device formed thereon, the first semiconductor device having a first gate trench and the second semiconductor device having a second gate trench; sequentially forming a high dielectric constant (high-k) gate dielectric layer and a multiple metal layer on the substrate; forming a first work function metal layer in the first gate trench; performing a first pull back step to remove a portion of the first work function metal layer from the first gate trench; forming a second work function metal layer in the first gate trench and the second gate trench; and performing a second pull back step to remove a portion of the second work function metal layer from the first gate trench and the second gate trench.