A thin film transistor array panel that includes: a substrate; a gate electrode disposed on the substrate; a semiconductor layer disposed on the substrate; a gate insulating layer disposed between the gate electrode and the semiconductor layer; a source electrode disposed on the semiconductor layer and a drain electrode facing the source electrode; a metal oxide layer covering the source electrode and the drain electrode; and a passivation layer covering the source electrode, the drain electrode, and the metal oxide layer, wherein the source electrode and the drain electrode include a first material and a second material which is added to the first material and metal included in the metal oxide layer is formed by diffusing the second material.