508 the channel layer 506 the wiring layer 511 and the passivation film 509 were measured it was confirmed that they were 80 or more at a visible range a sixth embodiment of the method of manufacturing an oxide semiconductor thin film transistor according to the present invention will be described with reference to fig1 to 18 the method of manufacturing an oxide semiconductor thin film transistor of this embodiment is for a bottom gate bottom contact structure characterized in that the pattern of a light blocking film 602 formed on the rear side of a substrate 601 is a negative pattern for source and drain electrodes 607 the light blocking film 602 is first formed on the rear side of the substrate 601 in the same manner as in the first embodiment the light blocking film 602 is shaped into a negative mask pattern for source and drain electrodes by photolithography and etching then a conductive film for a gate electrode 603 having a thickness of 20 to 200 nm is formed on the front side of the substrate 601 by sputtering plasma enhanced cvd pecvd or coating in the same manner as in the first embodiment in this embodiment a conductive film for the gate electrode 603 having a thickness of 70 nm is formed from ito by sputtering at a gas pressure of 0 5 pa ar 2 o 2 a.