We report some results the drain current characteristics of AlGaN/GaN HEMT(High Electron Mobility Transistor). on are simulated by changing the different device parameters such as Al content x and the barrier thickness for different values of the gate voltage using Tcad-Silvaco numerical simulation software. Drift-diffusion model has taken for simulating the proposed device. we use SiC as a substrate for this structure, The channel is made of GaN and source-drain spacing is 1 µm.