Multijunction systems are a promising alternative to overcome the efficiency limit of single-junction cells. A comparison between the two connection schemes, tandem and 4-terminal, is necessary for the development of the applications of this technology. To this purpose, we employed a Monte Carlo simulation algorithm, validated on experimental data, to evaluate the power conversion efficiency of a multijunction system in both configurations by obtaining the absorption spectrum of each layer and calculating the current-voltage characteristics for different thicknesses of each layer in the top cell.