Provided are an integrated circuit device and a method of manufacturing the same. The integrated circuit device includes: a semiconductor substrate; a device isolation layer defining an active region of the semiconductor substrate; a gate insulating layer on the active region; a gate stack on the gate insulating layer; a spacer on a sidewall of the gate stack; and an impurity region provided on both sides of the gate stack, wherein the gate stack includes a metal carbide layer and a metal layer on the metal carbide layer, wherein the metal carbide layer includes a layer having a carbon content of about 0.01 at % to about 15 at %.