A method is described for the detection of DNA hybridization on porous Si thin film, based upon the pairing of oligonucleotide chemistry and the silicon nano-technologies. A porous Si thin film with a pore diameter of approximately 25 nm was synthesized by anodizing a highly doped, n-type Si crystal in a dilute hydrofluoric acid (HF) solution. The surface of pores in the porous Si film was converted to the DNA-modified surface, on which single-stranded DNA molecules are covalently attached. Infrared spectromicroscopy was employed to monitor the hybridization of DNA immobilized on the pore surface with its complementary DNA. In our method, labeling of target DNA with fluorophore probes is not necessary. We demonstrate that DNA hybridization on porous Si thin film can be detected with high sensitivity by analyzing IRAS spectral profiles, suggesting potential utility of our method in DNA sensing chips.