Series-connected multi-junction solar cells have a number of important advantages over single junction cells because of the high open circuit voltage, e.g., the reduction of the series resistance effects in the context of system design and the suitability to the consumer electronic photo-cells. The Schottky barrier type and p-n homojunction type monolithic GaAs solar cell arrays were fabricated on (100) Cr-doped semi-insulating GaAs wafer with 5 µm n-GaAs epitaxial layer by using the usual photolithographic technique. The solar cell arrays exhibit V oc=3.0 V, η=7.5% for the 5 adjacent Schottky barrier type cell array and V oc=3.2 V, η=8.4% for the 4 adjacent p-n homojunction type cell array under simulated AM1 insolation, respectively.