Bandgap engineering of TiO2 is a substantial strategy for efficient water splitting in the visible light range. Introducing dopants and hydrogenation have been found effective for that purpose. In this paper, we report the development of a hierarchical three dimensional TiO2–Si nanowire (NW)-based photoelectrochemical (PEC) anode with visible light photochemical activity. The TiO2 NWs were synthesized using a surface reaction-limited pulsed chemical vapor deposition method (SPCVD) with unbalanced TiCl4 and H2O precursors. Dangling Ti–Cl and Ti–OH groups inside TiO2 NW crystals were suggested to be the reason for band narrowing and visible light absorption. The NW structure with a large aspect ratio was formed via the oriented attachment mechanism, which offered a super-high surface area density. This in situ crystal decoration approach opens a new window to tailoring electrical properties of TiO2 for wider spectrum solar energy harvesting and conversion.