A method of manufacturing a monolithic ink-jet printhead includes a heating element which generates bubbles by heating ink is formed on a surface of the substrate, and a negative photoresist which is coated to a predetermined thickness on the substrate on which the heating element is formed. Next, a portion, which forms a sidewall of an ink passage forming wall surrounding an ink chamber and a restrictor, of the negative photoresist is flush exposed to light and cured using a first photomask in which patterns of the ink chamber and the restrictor of the ink passage are formed. Subsequently, a second portion which forms an upper wall of the ink passage forming wall of the negative photoresist is exposed to the light using a second photomask in which the pattern of a nozzle is formed, and the second portion is exposed to the light by only a predetermined thickness. Last, an uncured portion of the negative photoresist is dissolved and removed using solvent. An ink-jet printhead whose elements are monolithically formed by a simplified process using a single negative photoresist can be manufactured.