In this paper we propose and simulate a new Heterostructure MESFET, Called δ-doped LDD HMESFET. To improve carrier velocity in vicinity of the source in channel of GaAs MESFET, one can replace source with AlxGa 1-x As. By increasing Al content, discontinuity of hetero-interface could be increased. Therefore, the velocity increases in the low field. However, increasing Al mole fraction in excess of some value forces the current to reduce, due to DX centers. To avoid this reduction, we suggest taking the advantage of ?-doped the source-channel hetero-interface. This increase discontinuity of hetero-interface, which is equivalent to increasing Al content. In this paper, we simulate the proposed transistor structure and compare it with the one proposed in , ignoring DX centers. In this comparison, we show that the average electron velocity in both transistors is identical.