A high electron mobility transistor (HEMT) includes a buffer layer, a carrier transit layer, a carrier supply layer, a gate, a source electrode and a drain electrode. The buffer layer is on a substrate. The carrier transit layer is on the buffer layer. The carrier supply layer is on the carrier transit layer. The gate is on the carrier supply layer. The source electrode and the drain electrode are at two opposite sides of the gate, wherein each of the source electrode and the drain electrode includes a conductive layer and a conductive oxide layer stacked from bottom to top.