A thin film transistor array panel includes: a gate conductor disposed on a substrate and including a gate line and a gate electrode, a semiconductor layer overlapping the gate electrode and including an oxide semiconductor, a data conductor including a data line intersecting the gate line, a source electrode connected to the data line, and a drain electrode facing the source electrode, a sidewall covering side surface parts of the drain electrode and the source electrode adjacent to a channel region of the semiconductor layer, and a passivation layer covering the source electrode, the drain electrode, and the sidewall.