A novel micromechanical infrared (IR) radiation sensor has been developed using commercially available piezoresistive microcantilevers. Microcantilevers coated with a heat absorbing layer undergo bending due to the differential stress between the top layer (coating) and the substrate. The bending causes a change in the piezoresistance and is proportional to the amount of heat absorbed. The microcantilever IR sensor exhibits two distinct thermal responses: a fast one (<ms) and a slower one (∼10 ms). A noise equivalent power (at a modulation frequency of 30 Hz) was estimated to be ∼70 nW/Hz1/2. This value can be further reduced by designing microcantilevers with better thermal isolation that can allow microcantilevers to be used as uncooled IR radiation detectors.