A method for the preparation of composites that allow the growth of ZnO nanorod structures on the full surface of porous silicon (polished surface, pore walls, and pore bottoms) is presented. The porous silicon is obtained by electrochemical etching of P-type silicon (100). The nanorods were grown in two steps: a sol–gel method and an oil bath method. The morphology of ZnO nanorods at different concentrations of the growth solution was investigated using scanning electron microscopy. X-ray diffraction confirmed the formation of ZnO hexagonal fibrous zincite structures. UV–Vis absorption spectroscopy confirmed that the composites possess good light absorption in the broad spectral region. In the wavelength range of 300 to 400 nm, the light absorption value of the porous silicon/zinc oxide (porous Si/ZnO) nanorods was increased by ~25% compared to that of the porous Si/ZnO films. The photoluminescence spectra confirmed the luminescence performance of the composites. Finally, the optical properties of the composites were further verified by simulation calculations.