A TFT structure having sufficiently low resistance wiring is provided, in which characteristic defects thereof caused by undercuts in a barrier metal layer can be prevented, the undercuts formed in a step for processing a source and a drain electrode composed of copper. The TFT structure of the present invention comprises a gate electrode on a glass substrate, a gate insulation film, a semiconductor active layer disposed on the gate insulation film so as to oppose the gate electrode, ohmic contact layers formed on both edge portions of the semiconductor active layer, and a source and a drain electrode connected to the semiconductor active layer via the respective ohmic contact layers. In addition, the source electrode and the drain electrode are formed of copper, and barrier metal layers are formed on the bottom surfaces of the source electrode and the drain electrode above areas at which the upper surfaces of the respective ohmic contact layers are located.