Abstract: A plurality of heaters are provided on a silicon substrate in a plurality of individual ink channels. Each heater is constructed from a thin-film resistor and a thin-film conductor. The thin-film resistor is formed with an electrical insulation layer at its upper surface. The electrical insulation layer is formed through subjecting the thin-film resistor to a high-temperature thermal oxidation process. The thin-film resistor formed with the electrical insulation layer may be covered with an additional insulation layer of a thickness substantially equal to the thin-film resistor.