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SiCr-based thin-film resistors with low temperature coefficient of resistance (TCR) have been integrated in a 0.8-μm BiCMOS technology in a dual thin-film structure, with a heater close to the thin-film resistor. Such a structure allows modifying the thin-film resistance by applying electric pulses to the heater (trimming). The morphology and the electrical properties of the as-deposited and modified thin-film resistors have been studied through transmission electron microscopy analyses and electrical measurements as a function of temperature. Structural analyses have shown the formation of Cr-rich layers at the interfaces. The experimentally observed resistance reduction upon trimming and the TCR variation have been both successfully reproduced by considering the effective medium approximation and by treating the film as a mixture of two materials with different compositions and conductivities.