A thin film transistor (TFT) substrate is provided in which a sufficiently large contact area between conductive materials is provided in a contact portion and a method of fabricating the TFT substrate. The TFT substrate includes a gate interconnection line formed on an insulating substrate, a gate insulating layer covering the gate interconnection line, a semiconductor layer arranged on the gate insulating layer, a data interconnection line including a data line, a source electrode and a drain electrode formed on the semiconductor layer, a first passivation layer formed on the data interconnection line and exposing the drain electrode, a second passivation layer formed on the first passivation film and a pixel electrode electrically connected to the drain electrode. An outer sidewall of the second passivation layer is positioned inside an outer sidewall of the first passivation layer.