A TFT and a passivation film are formed on a transparent substrate and thereafter the passivation film is annealed. When measuring drain currents of a TFT at a fixed turn-on voltage (Von) and a fixed turn-off voltage (Voff), although performance of a TFT annealed (solid line) rarely changes, performance of a TFT not annealed (dashed line) changes to a large extent, in more detail, drain current drastically decreases in accordance with the change of TFT performance. This phenomenon means that on-resistance of a TFT not annealed is being increased to a great extent.