A transistor is provided that includes a silicon layer including a source region and a drain region, a gate stack disposed on the silicon layer between the source region and the drain region, and a sidewall spacer disposed on sidewalls of the gate stack. The gate stack includes a first layer of high dielectric constant material, a second layer comprising a metal or metal alloy, and a third layer comprising silicon or polysilicon. The sidewall spacer includes a high dielectric constant material and covers the sidewalls of at least the second and third layers of the gate stack. Also provided is a method for fabricating such a transistor.