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We discuss the design, integration and testing of thermal components in a microfluidic device designed for on-chip genetic sample preparation. A typical microdevice must perform several operations to be capable of analyzing a sample of body fluid (blood, urine, saliva), extracting DNA from concentrated cells, hybridization, purifying and amplifying DNA, and finally detecting DNA fragments of interest. Reduction of the sample volume down to a few μLs and improvement of the ramp times between temperature steps makes micro-PCR devices desirable. Thermal components such as heaters and resistive thermal devices (RTDs) are fabricated as an integral part of a complete genetic sample preparation micro-system. The ability to precisely control the temperature is a critical component of most microfluidic devices intended for on-chip genetic sample preparation Devices were fabricated and demonstrated a temperature variation of ∼1°C over the entire sample volume. The design of a device, including chamber dimensions, and placement of the heating and cooling elements is presented. The results of temperature cycling experiments are shown. We have measured a heating rate of ∼2.4°C/s and a cooling rate of ∼2.0°C/s for devices tested under active heating/cooling control. A brief overview of relevant microfabrication methods is also presented.