An integrated circuit (IC) device includes: a channel region that extends on the substrate to penetrate a plurality of word lines; a bit line contact pad that contacts an upper surface of the channel region; a bit line that contacts the bit line contact pad and extends on the bit line contact pad in a direction parallel to the main surface of the substrate; a common source line that partially fills a word line cut region and has a height lower than that of the channel region; and a common source via contact that contacts an upper surface of the common source line in the word line cut region.