The observation of spectral components of the power dissipated by devices and circuits in integrated circuits (IC) by temperature measurements is limited by the bandwidth of either the temperature transducer or the intrinsic cut-off frequency provided by the thermal coupling inside the chip. In this paper, we use a heterodyne method to observe the high-frequency behavior of circuits and devices by means of low-frequency lock-in temperature measurements. As experimental results, two applications of the technique are presented: detection of hot spots in ICs activated by high-frequency electrical signals and the observation of the frequency response of an integrated resistor through temperature measurements. The heterodyne method has been used in this paper with four different measurement techniques: embedded differential BiCMOS temperature sensor, laser reflectometer, laser interferometer and internal IR laser deflection meter
