There has been a tremendous research effort in recent years to move DC-DC converters on chip for enhanced performance. However, a major limiting factor to implement on-chip inductive DC-DC converters is the large area overhead induced by spiral inductors. Towards this, we use through-silicon-vias (TSVs), a critical enabling technique in three-dimensional (3D) integrated systems, to implement on-chip inductors for DC-DC converters. While TSV inductors are inferior compared with conventional spiral inductors due to substrate loss for RF applications, it is not the case for DC-DC converters, which operate at relative low frequency. We will use a basic buck converter and an interleaved converter with magnetic coupling as examples to demonstrate this. Experimental results show that by replacing conventional spiral inductors with TSV inductors, with almost the same efficient and output voltage, up to 4.3x and 3.2x inductor area reduction can be achieved for the buck converter and the interleaved converter with magnetic coupling, respectively. In addition, with TSV inductors, the output voltage ripple is also reduced by 58.8% for the interleaved converter with magnetic coupling.