Hierarchical structures, with a high mass-loading of nanostructured lithium (Li) storage medium grafted upon large trunk framework, represent a novel approach towards high capacity and stable Li-ion batteries. We here report a new hierarchical structure of crystalline Si nanowires (c-Si NWs) grafted upon ultra-long tin dioxide (SnO2) NW trunks, where the latter frame up a large, conductive and stable architecture (i) to achieve a high mass-loading of c-Si NWs for Li-ion storage and (ii) to guarantee a good electric contact and fast charging process. The Si NWs branches are produced via a low-temperature vapor-liquid-solid (VLS) growth catalyzed by Sn droplets produced during a simple H2 plasma treatment upon the SnO2 trunks. Compared to other Si or SnO2 NW-based anodes structures, the c-Si/SnO2 NWs hierarchical structure demonstrates an outstanding performance with a high mass-load (~1.5mg/cm2) and a high areal capacity (~1.8mAh/cm2) after 100 cycles, without the use of any additional conductive polymer binder, highlighting the unique synergistic benefit of this hierarchical structure in boosting simultaneously the capacity and stability of Si-loaded Li-ion batteries.