A thin film transistor substrate includes a thin film transistor of a first conductivity type, a semiconductor layer having a channel region of the first conductivity type placed between the source/drain regions, a gate electrode formed to an opposite face to the semiconductor layer with an gate insulating film interposed therebetween, an opening in the gate electrode corresponding to both edges in a channel width direction of the channel region. In the channel region corresponding to the opening, a highly concentrated impurity region having a higher impurity concentration of the first conductivity type than the channel corresponding to the gate electrode is formed.