In a liquid crystal display (LCD) device having a thin film transistor (TFT), the TFT includes a source electrode, a drain electrode and a semiconductor layer. At least one of the source electrode and drain electrode includes a first layer including copper and a second layer forming an oxide layer and covering the first layer. The semiconductor layer has a substantially linear current-voltage relationship with said source electrode or drain electrode including said first and second layers, when a voltage is applied between the semiconductor layer and said source electrode or drain electrode.