in a method of electrically testing an active matrix substrate having a plurality of semiconductor switching devices , a row group of a plurality of parallel conductors and a column group of a plurality of parallel conductors , a gate electrode of each of the semiconductor switching devices being connected to one of the conductors of the row group , and a source electrode of each of the semiconductor switching devices being connected to one of the conductors of the column group , there are provided the steps of short - circuiting the conductors of the row group at both ends thereof ; short - circuiting the conductors of the column group at both ends thereof ; applying a predetermined voltage between the row and column groups of the conductors ; and measuring a current flowing from the row group to the column group of the conductors . moreover , in determining whether the active matrix substrate is defective , there is also provided the step of determining whether the following formula is satisfied or not : i . sub . 1 ≦ n × i . sub . 2 where i 1 is current measured by the step of measuring ; i 2 is known driving current of each of the semiconductor switching device ; and n is a constant .