A method of manufacturing an inkjet printhead, comprising: disposing a heater for heating an ink and an electrode for supplying a current to the heater on a substrate; disposing a channel forming layer which defines an ink channel by coating a first negative photoresist composition on the substrate on which the heater and the electrode are disposed and then patterning the coated composition using a photolithography process; disposing a sacrificial layer by coating a positive photoresist composition or a non-photosensitive soluble polymer composition on the substrate on which the channel forming layer is disposed such that the coated composition completely covers the channel forming layer; planarizing top surfaces of the channel forming layer and the sacrificial layer using a polishing process; disposing a nozzle layer having a nozzle by coating a second negative photoresist composition on the channel forming layer and the sacrificial layer and patterning the coated composition using a photolithography process; forming an ink feed hole in the substrate; and removing the sacrificial layer; wherein a solvent included in the positive photoresist composition or in the non-photosensitive soluble polymer composition which is used to form a sacrificial layer has a different polarity from that of a solvent included in at least one of the first and second negative photoresist compositions, characterized in that the solvent included in the positive photoresist composition or in the non-photosensitive soluble polymer composition has a lower polarity than the solvent included in at least one of the first and second negative photoresist compositions. disposing a heater for heating an ink and an electrode for supplying a current to the heater on a substrate; disposing a channel forming layer which defines an ink channel by coating a first negative photoresist composition on the substrate on which the heater and the electrode are disposed and then patterning the coated composition using a photolithography process; disposing a sacrificial layer by coating a positive photoresist composition or a non-photosensitive soluble polymer composition on the substrate on which the channel forming layer is disposed such that the coated composition completely covers the channel forming layer; planarizing top surfaces of the channel forming layer and the sacrificial layer using a polishing process; disposing a nozzle layer having a nozzle by coating a second negative photoresist composition on the channel forming layer and the sacrificial layer and patterning the coated composition using a photolithography process; forming an ink feed hole in the substrate; and removing the sacrificial layer; wherein a solvent included in the positive photoresist composition or in the non-photosensitive soluble polymer composition which is used to form a sacrificial layer has a different polarity from that of a solvent included in at least one of the first and second negative photoresist compositions, characterized in that the solvent included in the positive photoresist composition or in the non-photosensitive soluble polymer composition has a lower polarity than the solvent included in at least one of the first and second negative photoresist compositions.