Smart stack is a handy method to construct multi-junction tandem through the interconnection of different types of solar cells using a Pd nanoparticle array as a bonding mediator. In this study, a triple-junction cell was fabricated from InGaP/GaAs and crystalline Si subcells using the smart stack method, which resulted in a conversion efficiency of 23.2%. The EQE analysis of the smart stack cell was also carried out, suggesting that higher efficiencies are feasible through better current matching among the subcells.