A semiconductor structure and a method of fabricating the same are disclosed. The semiconductor structure comprises an active region over a substrate defining a top surface and a gate structure embedded in the active region. In a cross section of the active region, the gate structure includes a conductive feature having a first width buried in the active region and reaching a first depth therein; an insulating cap having a second width arranged above the conductive feature in the active region and reaching a second depth therein; and a dielectric liner arranged between the active region and the conductive feature. The first width is smaller than the second width.