A transistor manufacturing method includes forming a source electrode and a drain electrode on a substrate, forming a layer including an insulator layer to cover the source electrode and the drain electrode, and forming a gate electrode on the layer including the insulator layer, wherein the forming the gate electrode includes forming a plating base film, forming a protection layer of the plating base film, forming a photoresist layer on the protection layer to expose the photoresist layer with desired patterning light, causing the exposed photoresist layer to come into contact with a developer to remove the photoresist layer and the protection layer until the plating base film is uncovered corresponding to the patterning light, and after depositing a metal on the uncovered plating base film, causing an electroless plating solution to come into contact with the plating base film to perform electroless plating.