A DNA chip includes a substrate, at least one first electrode and at least one second electrode on the substrate, the first electrode and the second electrode being opposite to and separated from each other, multiple oligonucleotide probes, one end of the oligonucleotide probes being immobilized on the first electrode, and a charge-carrier transport layer on the second electrode, the charge-carrier layer contacting an other end of the oligonucleotide probes.