Semiconductor devices

A semiconductor device includes a substrate; an active region extending in a first direction on the substrate; a gate structure extending in a second direction on the substrate and including a gate electrode; a source/drain region provided on the active region on at least one side of the gate structure; an interlayer insulating layer covering the gate structure; a first contact structure connected to the source/drain region on at least one side of the gate structure; and a gate contact structure passing at least partially through the interlayer insulating layer and connected to the gate electrode, wherein the gate contact structure includes: a first layer including a conductive material; a second layer provided on the first layer, spaced apart from the interlayer insulating layer by the first layer, and including first impurities; and a third layer provided on the second layer and including second impurities.