Provided is a method for manufacturing a dual gate in a semiconductor device. The method includes forming a gate insulating layer and a gate conductive layer on a semiconductor substrate, forming a diffusion barrier layer on the gate conductive layer, forming a barrier metal layer on the diffusion barrier layer, depositing a first gate metal layer on the barrier metal layer, forming a metal nitride barrier layer on a surface of the first gate metal layer by supplying nitrogen (N2) plasma on the first gate metal layer, forming a second gate metal layer on the metal nitride barrier layer, and forming a hard mask layer on the second gate metal layer.