the method comprising:

forming a pair of source/drain regions over a substrate and a gate electrode between the pair of source/drain regions;

forming a lower inter-layer dielectric (ILD) layer over the pair of source/drain regions and surrounding the gate electrode;

etching back the gate electrode to form a recess region from top of the lower ILD layer;

forming a gate capping layer on the gate electrode within the recess region;

forming a lower source/drain contact on a source/drain region of the pair of source/drain regions;

forming a source/drain capping layer on the lower source/drain contact;

forming a gate electrode contact through the gate capping layer and reaching on the gate electrode; and

forming a contact structure comprising a first portion and a second portion, wherein the first portion is disposed through the gate capping layer, and wherein the second portion is disposed through the source/drain capping layer.