A printhead integrated circuit that has a plurality of nozzles formed on a frontside of a monolithic wafer substrate, the nozzles being arranged in rows extending longitudinally along the substrate. Each nozzle has a respective nozzle inlet extending partially through the monolithic wafer substrate. The integrated circuit also has a plurality of ink supply channels defined in a backside surface of the monolithic wafer substrate which extend longitudinally along the backside of the substrate. Each ink supply channel is deep enough to meet the nozzle inlets such that ink fed to the backside surface of the substrate is supplied to the nozzles on the frontside. The nozzles supplied with ink from one of the ink supply channels are different to the nozzles supplied with ink by another of the ink supply channels such that different ink colors are simultaneously printed. Each ink supply channel is separated into channel sections by one or more transverse walls that structurally stiffen the monolithic wafer substrate.