The design, fabrication and evaluation of a low-cost and low-power, continuous-flow microfluidic device for DNA amplification by polymerase chain reaction (PCR) with integrated heating elements, on a commercially available thin polymeric substrate (Pyralux (R) Polyimide), is presented. The small thermal mass of the chip, in combination with the low thermal diffusivity of the polymeric substrate on which the heating elements reside, yields a low power consumption PCR chip with fast amplification rates. A flow-through mu PCR device is designed and fabricated using flexible printed circuit (FPC) technology on a foot-print area of 8 cm x 6 cm with a meandering microchannel realized at a very small distance (50 mu m) above 3 independently operating resistive (copper) serpentine microheaters, each one defining one of the three PCR temperature zones. The 145 cm-long microchannel is appropriately designed to cross the alternating temperature zones as many times as necessary for the DNA sample to perform 30 PCR cycles. Numerical computations lead the design so that there is no thermal crosstalk between the 3 zones of our chip and indicate excellent temperature uniformity in each zone. In addition, the total power consumption during the chip operation is calculated to be in the order of a few Watts, verified experimentally by means of thermal characterization of our heaters. Thermal camera measurements also verified the excellent temperature uniformity in the three thermal zones. An external, home-made temperature control system was utilized to maintain the heater temperatures in the designated values (+/- 0.2 degrees C). The PCR chip was validated by a successful amplification of a 90 base-pairs DNA template of the mouse GAPDH housekeeping gene within 5 min.