Transistor devices having buried interconnection line below source/drain regions and one or more protective layers covering lower surfaces of gate structures

Abstract

A semiconductor device includes an active region extending in a first direction; a device isolation layer on side surfaces of the active region and defining the active region; a gate structure intersecting the active region on the active region and extending in a second direction; source/drain regions in regions in which the active region is recessed, on both sides of the gate structure; first protective layers between the device isolation layer and the gate structure; and a buried interconnection line below the source/drain regions and connected to one of the source/drain regions through an upper surface of the buried interconnection line.