A low gate resistance high-k metal gate transistor device is formed by providing a set of gate stacks (e.g., replacement metal gate (RMG) stacks) in a trench on a silicon substrate. The gate stacks in the trench may have various layers such as: a high-k layer formed over the substrate; a barrier layer (formed over the high-k layer; a p-type work function (pWF) layer formed over the barrier layer; and an n-type work function (nWF) layer formed over the pWF layer. The nWF layer will be subjected to a nitrogen containing plasma treatment to form a nitridized nWF layer on the top surface, and an Al containing layer will then be applied over the gas plasma treated layer. By utilizing a gas plasma treatment, the gap within the trench may remain wider, and thus allow for improved Al fill and reflow at high temperature (400° C.-480° C.) subsequently applied thereto.