There is disclosed an ink jet printhead which comprises a plurality of nozzles (3) and one or more heater elements (10) corresponding to each nozzle. Each heater element is configured to heat a bubble forming liquid in the printhead to a temperature above its boiling point to form a gas bubble (12) therein. The generation of the bubble causes the ejection of a drop (16) of an ejectable liquid (such as ink) through the respective corresponding nozzle, to effect printing. Each heater element is configured such that the energy applied to it to heat the bubble forming liquid to cause the ejection of a drop is less than that required to heat a volume of the ejectable liquid equal to the volume of such a drop, from an ambient temperature (being the temperature at which the bubble forming liquid enters the printhead) to the temperature of such a drop when it is ejected. The printhead thus has a self-cooling function.