A silicon nanoporous pillar array (Si-NPA) is a silicon hierarchical structure with regularlypatterned surface morphology. Through a heterogeneous reaction process, nanocrystallites ofcadmium sulfide (nc-CdS) were grown onto Si-NPA and a uniquely patterned nanocompositestructure (CdS/Si-NPA) was obtained. The nc-CdS, whose average size was evaluated to be∼25 nm, mainly grew at two typical sites of the Si-NPA. One was the top sites ofthe porous pillars where nc-CdS clusters were formed, and the other was thevalley sites surrounding the porous pillars where nc-CdS rings were formed. Thenc-CdS was proved to be separated from the Si-NPA substrate by a thin layer ofSiO2 with athickness of ∼1.3 nm. In addition to the two red photoluminescence (PL) bands observed in the Si-NPA, a green PL bandpeaked at ∼495 nm was observed in CdS/Si-NPA when it was excited by 370 nm wavelength ultravioletlight. Based on these experimental results, the green and red PL bands of CdS/Si-NPAwere attributed to the radiative recombination of the excitons occurring in nc-CdS andSi-NPA separately.