A method for manufacturing a dual work function semiconductor device includes forming a first silicon oxide layer on a substrate and forming a first hafnium-containing dielectric material layer on the first silicon oxide layer. The method further includes forming an aluminum-containing dielectric material layer on the first hafnium-containing dielectric material layer and performing a thermal treatment to intermix the silicon oxide layer, the first hafnium-containing dielectric material layer and the aluminum-containing dielectric material layers. This results in an intermixing dielectric layer containing hafnium, aluminum, silicon, and oxygen. The method further includes forming a first metal-containing conductive layer on the intermixing dielectric layer and patterning the first metal-containing conductive layer and the intermixing dielectric layer, thereby forming a first gate stack in a first region.