HEMT suffers from parasitic resistance (Rsd) and capacitance(Cgd) effects with the shrinking of channel length, leading to degraded performance in logic and RF applications. A new while simple method to extract parasitic RC has been proposed to construct accurate transport parameters in HEMTs. In comparison to the constant-Rsd method, this new voltage dependent method provides more convincing results, especially for very short channel devices. On the other hand, an accurate Cgd correction method has also been incorporated to adequately represent the mobility. Finally, a guideline to design high performance HEMTs has been proposed.