The extensive application of humidity sensors has greatly stimulated the study on high-performance humidity-sensing materials. In the paper, we report that a prototype humidity sensor was prepared by growing cadmium sulfide (CdS) on silicon nanoporous pillar array (Si-NPA) through a successive ionic layer adsorption and reaction method followed by immersing the samples in the solution of lithium chloride (LiCl). It was demonstrated that through the immersion treatment, the humidity-sensing properties including the response and its linearity, response and recovery time, hysteresis, and measuring reproducibility and stability were improved significantly. These results indicated that LiCl-immersed CdS/Si-NPA might be a promising material for fabricating humidity sensors applied to medium and low humidity range.