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Four differential temperature sensors, two passive and two active, designed and fabricated in a 0.35-m standard CMOS technology, are presented and characterized. Passive sensors are based on integrated thermopiles. Each one consists of eight thermocouples (16 strips) serially connected: poly1-poly2 for the first thermopile and poly1-P+diffusion for the second one. The active sensors are based on differential amplifiers, one with single-ended output and the other with differential output. Lateral parasitic bipolar transistors are used as temperature transducer devices. Both simulated and experimental characterizations are presented. The high sensitivity of active differential temperature sensors proves the feasibility of such sensors to observe the power dissipated by devices and circuits embedded in the same silicon die, with applications to the test and characterization of circuits, packaging characterization and compensation of thermal gradients, among others.