US Patent 9508810 FET with air gap spacer for improved overlap capacitance

A semiconductor device and method of forming a semiconductor device including a semiconductor substrate, a gate stack extending from the semiconductor substrate, wherein the gate stack includes a gate conductor layer, and at least two gate spacers adjacent to each side of the gate stack. The semiconductor device also includes a source/drain region on each side of the spacers, wherein the source/drain regions are adjacent to the semiconductor substrate, an ILD layer adjacent to outer surfaces of the two spacers, wherein a height of the ILD layer is level with a height of the gate stack, and an air gap positioned beneath each spacer.