Integrated circuit (IC) packages employing front side back-end-of-line (FS-BEOL) to back side back-end-of-line (BS-BEOL) stacking for three-dimensional (3D) die stacking. To facilitate providing additional electrical routing paths for die-to-die interconnections between stacked IC dice in the IC package, a BS-BEOL metallization structure of a first die of the stacked dice of the IC package is stacked adjacent to a FS-BEOL metallization structure of a second die of the stacked IC dice. Electrical routing paths for die-to-die interconnections between the stacked IC dice are provided from the BS-BEOL metallization structure of the first die to the FS-BEOL metallization structure of the second die. It may be more feasible to form shorter electrical routing paths in the thinner BS-BEOL metallization structure than in a FS-BEM metallization structure for lower-resistance and/or lower-capacitance die-to-die interconnections for faster and/or compatible performance of semiconductor devices in the IC dice.