As the convergence of multiple functions in a single electronic device drives current electronic trends, the need for increasing integration density is becoming more emphasized than in the past. To keep up with the industrial need and realize the new system integration law, three-dimensional (3-D) integration called System-on-Package (SoP) is becoming necessary. However, the commercialization of 3-D integration should overcome several technical barriers, one of which is the difficulty for the electrical design of interconnections. The 3-D interconnection design is difficult because of the modeling challenge of electrical coupling from the complicated structures of a large number of interconnections. In addition, mixed-signal design requires broadband modeling, which covers a large frequency spectrum for integrated microsystems. By using currently available methods, the electrical modeling of 3-D interconnections can be a very challenging task. This dissertation proposes a new method for constructing a broadband model of a large number of 3-D interconnections. The basic idea to address the many interconnections is using modal basis functions that capture electrical effects in interconnections. Since the use of global modal basis functions alleviates the need for discretization process of the interconnection structure, the computational cost is reduced considerably. The resultant interconnection model is a RLGC model that describes the broadband electrical behavior including losses and couplings. The smaller number of basis functions makes the interconnection model simpler, and therefore allows the generation of network parameters at reduced computational cost. Focusing on the modeling of bonding wires in stacked ICs and through-silicon via (TSV) interconnections, this research validates the interconnection modeling approach using several examples from 3-D full-wave EM simulation results.