Rigorous coupled wave analysis (RCWA) simulation was used to model the absorption in periodic arrays of GaAs0.73P0.27 nanowires (NWs) on Si substrates dependent upon the diameter (D), length (L), and spacing (center-to-center distance, or pitch, P) of the NWs. Based on this study, two resonant arrangements for a top NW array sub-cell having the highest limiting short-circuit current densities (Jsc) were found to be close to D = 150 nm, P = 250 nm and D = 300 nm, P = 500 nm, both featuring the same packing density of 0.28. Even though a configuration with thinner NWs exhibited the highest Jsc = 19.46 mA/cm2, the array with D = 350 nm and P = 500 nm provided current matching with the underlying Si sub-cell with Jsc = 18.59 mA/cm2. Addition of a rear-side In0.81Ga0.19As nanowire array with D = 800 nm and P = 1000 nm was found to be suitable for current matching with the front NW sub-cell and middle Si. However, with thinner and sparser In0.81Ga0.19As NWs with D = 700 nm and P = 1000 nm, the Jsc of the bottom sub-cell was increased from 17.35 mA/cm2 to 18.76 mA/cm2 using a planar metallic back surface reflector, thus achieving a current matching with the top and middle cells.