The HEMT includes a channel layer, a barrier layer, a drain, and a gate conductor. The barrier layer is disposed on the channel layer. The drain is disposed on the barrier layer. The gate conductor is disposed on the barrier layer. The channel layer includes a doped semiconductor structure overlapping with a top surface of the channel layer and having a bottom-most border that is located over a bottom-most surface of the channel layer and is spaced apart from the bottom-most surface of the channel layer. The doped semiconductor structure is located between the drain and the gate conductor.