Novel, 3D hierarchical Co3O4 twin-spheres with an urchin-like structure are produced successfully on the large scale for the first time by a solvothermal synthesis of cobalt carbonate hydroxide hydrate, Co(CO3)0.5(OH)·0.11H2O, and its subsequent calcination. The morphology of the precursor, which dominates the structure of the final product, evolves from nanorods to sheaf-like bundles, to flower-like structures, to dumbbell-like particles, and eventually to twin-spheres, accompanying a prolonged reaction time. A multistep-splitting growth mechanism is proposed to understand the formation of the 3D hierarchical twin-spheres of the precursor, based on the time effect on the morphologies of the precursor. The 3D hierarchical Co3O4 twin-spheres are further used as electrode materials to fabricate supercapacitors with high specific capacitances of 781, 754, 700, 670, and 611 F g−1 at current densities of 0.5, 1, 2, 4, and 8 A g−1, respectively. The devices also show high charge-discharge reversibility with an efficiency of 97.8% after cycling 1000 times at a current density of 4 A g−1.