A microfluidic device is described. The device comprises a flow channel; and at least one reaction chamber. The at least one reaction chamber comprises a chamber inlet connecting the at least one reaction chamber to the flow channel, a first region adjacent the chamber inlet, a second region spaced from the chamber inlet by the first region, a vent channel and a reaction reagent disposed on at least one inner surface of the second region. Also described is a PCR apparatus and a method of performing PCR.