In a method of manufacturing a TFT substrate in accordance with an exemplary aspect of the present invention, an intrinsic semiconductor film, an impurity semiconductor film, and a conductive film for source lines are formed in succession, and a resist having a thin-film portion and a thick-film portions is formed on the conductive film for source lines. Then, etching is performed by using the resist as a mask, and after that, a part of the conductive film for source lines is exposed by removing the thin-film portion of the resist. Next, the exposed conductive film for source lines is etched by using the thick-film portions of the resist a mask, so that the impurity semiconductor film is exposed. Then, by etching the exposed impurity semiconductor film, a back channel region of a TFT 108 is formed. Further, a dummy back channel region 18a, which is irrelevant to the operation of the finished product, is also formed in a portion other than the TFT 108 region.