Some commercial 10kΩ/sq. thick-film resistors based on RuO 2 , ruthenates or a mixture of RuO 2 and ruthenates, were evaluated. The resistors were fired at different temperatures to determine the influence of firing temperature on the electrical and microstructural characteristics. The conductive phase in the resistors (RuO 2 , ruthenate, and a mixture of RuO 2 and ruthenate) was determined with X-ray powder-diffraction analysis. The microstructures of the thick-film resistors were analysed with scanning electron microscopy, transmission electron microscopy and energy-dispersive X-ray analysis. The temperature coefficients of resistivity, noise indices and gauge factors were measured as a function of firing temperature. After long-term high temperature firing (6h at 950 o C) ruthenate transforms into RuO 2 coinciding with a significant increase of the temperature coefficients of resistivity.