Semiconductor devices are provided including a semiconductor substrate and a first interlayer insulating layer on the semiconductor substrate. A contact pad is provided in the first interlayer insulating layer and a second insulating layer is provided on the first interlayer insulating layer. A contact hole is provided in the second interlayer insulating layer. The contact hole exposes the contact pad and a lower portion of the contact hole has a protrusion exposing the contact pad. The protrusion is provided on the second interlayer insulating layer. A contact spacer is provided on inside sidewalls of the contact hole and fills the protrusion. A contact plug is provided in the contact hole. Related methods are also provided herein.