Integrated circuit (IC) devices are provided including a substrate having a first sidewall defining a first through hole that is a portion of a through-silicon via (TSV) space, an interlayer insulating layer having a second sidewall and a protrusion, wherein the second sidewall defines a second through hole providing another portion of the TSV space and communicating with the first through hole, and the protrusion protrudes toward the inside of the TSV space and defines an undercut region in the first through hole, a TSV structure penetrating the substrate and the interlayer insulating layer and extending through the first through hole and the second through hole, and a via insulating layer surrounding the TSV structure in the first through hole and the second through hole.