Disclosed herein are various embodiments of an improved metal gate structure for semiconductor devices, such as transistors. In one example disclosed herein, a transistor has a gate structure consisting of a gate insulation layer positioned on a semiconducting substrate, a high-k insulation layer positioned on the gate insulation layer, a layer of titanium nitride positioned on the high-k insulation layer, a layer of aluminum positioned on the layer of titanium nitride and a layer of polysilicon positioned on the layer of aluminum.