A thin-film semiconductor substrate includes a top-gate first TFT, a top-gate second TFT, and a data line (source line), in which the first TFT has a first semiconductor layer, a first gate insulating film, a first gate electrode, a first source electrode, a first drain electrode, and a first protection layer, the second TFT has a second semiconductor layer, a second gate insulating film, a second gate electrode, a second source electrode, a second drain electrode, and a second protection layer, the data line is connected to the first source electrode, the first drain electrode is an extension of the second gate electrode, and the second gate electrode is thinner than the data line.