A multi-layer device suitable for thermal cycling is set forth. The device is particularly suitable for performing a polymerase chain reaction (PCR). One embodiment includes a first layer (18), a second layer (20) adjacent to the first layer, and a third layer (22) adjacent to the second layer opposite the first layer. A continuous channel (54) is formed within the first layer (18), the second layer (20), and the third layer (22). The continuous channel (54) has a plurality of cycle segments, each of the cycle segments comprises a first portion (58) disposed within the first layer (18), a second portion (62) disposed within the third layer (22), and a third portion (66) disposed within the second layer (20). An integral or separate temperature source or sources (14), (16) may be provided to maintain the first layer (18) at a first temperature and the third layer (22) at a second temperature. Thermal conduction maintains the third layer (22) at a temperature between the first temperature and the second temperature.