Chip gel electrophoresis was explored for high-sensitivity detection of DNA by combining electrokinetic injection with transient isotachophoresis preconcentration (here named electrokinetic supercharging (EKS)). Low concentrations (0.2 mg/L) of DNA sample could be detected without fluorescence labeling using a conventional UV detector (at 260 nm). On a single-channel microchip, identification of PCR product was performed by exploiting both external and internal calibration methods. The deviation between the two calibration methods was about 3.6%, and the identified DNA fragment size matched with the predicted size of the template DNA. On the cross microchip the EKS preconcentration has also been achieved when changing the injection reservoir differing from the one used previously. The procedure was computer-simulated and the influence of the voltage applied to two-side reservoirs on sample preconcentration and dilution was also discussed.