Change in film properties, especially resistivity and the thermal dependence of resistance, that are due to differences in the thickness and the temperature of heat treatment of Ta-Si-C films developed as high resistivity materials were investigated. From these results, the mechanism of film thermal changes was discussed. Further, the effect of film thickness on the performance of Ta-Si-C thin film thermal printing heads was also investigated. The results show that; (1) a ln ρT-1/2 relationship between resistivity and temperature in Ta-Si-C thin films holds good over a wide temperature range from 293 to 873 K, (2) resistivity is dependent of film thickness when film thickness is less than 2000 (greater resistivity in thinner films), (3) the thermal dependence of resistance is dependent on film thickness when film thickness is less than 3000 (greater thermal dependence in thinner films), (4) resistivity is increased and thermal dependence of resistance is decreased by heat treatment below 400 , and that (5) excellent performance is achieved when Ta-Si-C thin films greater than 3000 in thickness are used as the thermal printing head resistor film.