A photoelectrochemical (PEC) cell made of metal-free carbon nitride (g-C3N4) @siliconnanowire(Si NW) arrays (denoted as Si NWs/g-C3N4) is presented in this work. The as-prepared photoelectrodes with different mass contents of g-C3N4have been synthesized via a metal-catalyzed electroless etching (MCEE), liquid atomic layer deposition (LALD) and annealing methods. The amount of g-C3N4on the Si NW arrays can be controlled by tuning the concentration of the cyanamide solution used in the LALD procedure. The dense and vertically aligned Si NWs/g-C3N4core/shell nanostructures were characterized by scanning electron microscopy (SEM), transmission electron microscopy (TEM), and X-ray diffraction (XRD). In comparison with FTO/g-C3N4and Si NW samples, the Si NWs/g-C3N4samples showed significantly enhanced photocurrents over the entire potential sweep range. Electrochemical impedance spectroscopy (EIS) was conducted to investigate the properties of the charge transfer process, and the results indicated that the enhanced PEC performance may be due to the increased photo-generated interfacial charge transfer between the Si NWs and g-C3N4. The photocurrent density reached 45 μA/cm2under 100 mW/cm2(AM 1.5 G) illumination at 0 V (vs. Pt) in neutral Na2SO4solution (pH ∼ 7.62). Finally, a systematical PEC mechanism of the Si NWs/g-C3N4was proposed.