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A novel bulk-micromachined test structure is presented for the fast and reliable determination of the lateral thermal conductivity of thin films. The device is composed of a heater resistor and thermocouples that are fabricated in polysilicon (poly-Si), and the associated processing and DC measurement procedures are straightforward. The validity of the method is supported by numerical simulations and verified by experimental determination of the lateral thermal conductivity of aluminum (Al), aluminum nitride (AlN), p-doped poly-Si, and silicon nitride (SiN) thin films. For Al, an average value of 217 W m-1 K-1 was found for 1-mum thick layers. For the other layers, a number of thicknesses were studied, and the increase of thermal conductivity with thickness was effectively detected: for AlN, values from 7 to 11.5 W m-1 K-1 were found, and for p-doped poly-Si, values went from 21 to 46 W m-1 K-1 for thicknesses from 0.15 to 1 mum. For SiN, a value of 1.8 was extracted for layers thicker than 0.5 mum.