Abstract: An electrical heating resistor of the type deposited on a substrate plate constituting the basis element of a thermal printing head. In order to concentrate the heat given off in the free surface of said heating resistor towards the paper to print, the invention provides for the deposition on the substrate of at least one layer having a relatively constant resistivity and then at least one surface layer with a non-linear resistivity and a negative temperature coefficient. Starting from a high value when cold, the resistance of the surface layer drops abruptly as soon as it reaches the triggering temperature, thus switching the heat resistor by command of a control circuit.