The present invention provides a thin film transistor substrate and a display device in which a decrease in the dry etching rate of a source electrode and drain electrode is not caused; no etching residues are generated; and a barrier metal can be eliminated between a semiconductor layer and metal wires such as the source and drain electrodes. The present invention is a thin film transistor substrate having a semiconductor layer 1, a source electrode 2, a drain electrode 3, and a transparent conductive film 4, in which the source electrode 2 and drain electrode 3 are formed by patterning by means of dry etching and comprises an Al alloy thin film comprising 0.1 to 1.5 atom % of Si and/or Ge, 0.1 to 3.0 atom % of Ni and/or Co, and 0.1 to 0.5 atom % of La and/or Nd, and the thin film transistor is directly connected with the semiconductor layer 1.