Microchips are constructed with photolithography technology and chemical synthesis. Microchip-based devices can be applied for separation, preparation and preconcentration of biological sample. The devices are also used for polymerase chain reaction or ligase chain reaction as the reaction vessels. The most attractive application is that the microchip immobilizing various oligonucleotide arrays can be used to detecting gene mutation. In addition, these compact arrays of probes may be used for ultrafast DNA sequencing. The fabrication, principle, characteristic and application of microchips were introduced.