A semiconductor device structure is provided. The semiconductor device includes a plurality of fins on a substrate, and a metal gate structure disposed on the plurality of fins. The metal gate structure includes a work function metal layer over the plurality of fins, a metal layer on the work function metal layer, and a metal oxide layer on the metal layer. A first portion of the metal oxide layer is formed within an area between adjacent fins from among the plurality of tins. An example benefit includes reduced diffusion of unwanted and/or detrimental elements from the first metal layer into its underlying layers and consequently, the reduction of the negative impact of these unwanted and/or detrimental elements on the semiconductor device performance.