Process integration of 4F2 DRAM array with peri-under-cell (PUC) architecture has been successfully demonstrated for the first time, employing vertical gate (VG) cell transistor and wafer bonding process. Fusion wafer bonding and inter-wafer contact techniques enabled wafer-to-wafer integration to provide robust electrical connections between cell and peripheral circuit wafers. Compared to conventional 2D DRAM, superior control over threshold voltage is achieved from back gate bias in VG cell transistor. Precise junction engineering by thermal annealing optimizes cell transistor performance.