According to example embodiments, a high electron mobility transistor (HEMT) includes a first semiconductor layer on a substrate and a second semiconductor layer on the first semiconductor layer. The first and second semiconductor layers define a recessed region. A semiconductor doped layer is in the recessed region of first and second semiconductor layers. A 2-dimensional electron gas (2DEG) region is at a portion of the first semiconductor layer adjacent to both sides of the semiconductor doped layer.