An inkjet printing system according to an exemplary embodiment of the present invention includes an inkjet printing chamber depositing ink on a substrate, and a drying chamber spaced from inkjet printing chamber by a predetermined interval and drying the ink by regulating a vapor pressure of a solvent of the ink deposited on substrate. The drying chamber is provided separately, and the vapor pressure of the solvent within the drying chamber is regulated, so that the drying speed of the ink is regulated so as to improve the crystallinity of the organic semiconductor.