An integrated circuit (IC) device includes a first substrate and a first structure on a front surface of the first substrate. The first structure includes a first interlayer insulating layer structure including a plurality of first conductive pad layers spaced apart from one another at different levels of the first interlayer insulating layer structure. The IC device includes a second substrate on the first substrate and a second structure on a front surface of the second substrate, which faces the front surface of the first substrate. The second structure includes a second interlayer insulating layer structure bonded to the first interlayer insulating layer structure. A through-silicon via (TSV) structure penetrates the second substrate and the second interlayer insulating layer structure. The TSV structure is in contact with at least two first conductive pad layers of the plurality of first conductive pad layers located at different levels.