A thin film transistor substrate, wherein the moving area of electrons between source and drain electrodes of a thin film transistor (TFT) is minimized, the moving distance of electrons is increased, and the sizes of capacitors defined by a gate electrode together with the respective source and drain electrodes are identical to each other so that an off current generated when the TFT is off can be minimized; a method of manufacturing the thin film transistor substrate; and a mask for manufacturing the thin film transistor substrate. Accordingly, it is possible to minimize an off current induced due to a phenomenon of electron trapping by light.