Abstract: Microwave power transistors made of conventional semiconductors have already approached their performance limit. In order to meet the future needs of wireless communication systems, research efforts are directed to wide bandgap semiconductors such as GaN. The combined merits of high power and high speed can be achieved using High Electron Mobility Transistors (HEMTs) made of AlGaN/GaN materials system. In this work, presents both one-dimensional and two-dimensional models to assess the static characteristics of AlGaN/GaN HEMT. Simulation results are presented to address the effect of various structure parameters on the drain I-V and transconductance characteristics. The physical parameters that affect the operation of the device is also investigated. The results can be used as guidelines to design ALGaN/GaN HEMT operating at high speed and having high transconductance. The results indicate that AlGaN/GaN HEMT fabricated with gate length of m 2 and gate width of m 25 may have a transconductance of 0.8 ms at V Vd 2 . The simulation results presented in this work are performed using MATLAB7 and MATHCAD5 software packages