A thin film transistor array panel includes a gate line, a gate insulating layer that covers the gate line, a semiconductor layer that is disposed on the gate insulating layer, a data line and drain electrode that are disposed on the semiconductor layer, a passivation layer that covers the data line and drain electrode and has a contact hole that exposes a portion of the drain electrode, and a pixel electrode that is electrically connected to the drain electrode through the contact hole. The data line and drain electrode each have a double layer that includes a lower layer of titanium and an upper layer of copper, and the lower layer is wider than the upper layer, and the lower layer has a region that is exposed. The gate insulating layer may have a step shape.