Nowadays, the technology computer aided design (TCAD) software has become an important and powerful tool for improving the efficiency of GaN power devices design and its optimization. The paper attempts to describe the features, advantages and applications of such approach. The limitations and calibration problems of technology simulation are also discussed. Furthermore, the possibility of using Silvaco TCAD tools for 2D-numerical simulation of GaN HEMT T-gate formation is demonstrated. The paper represents the results of simulation of several technological operations like mask formation, resist reflow and metal deposition and varying of process parameters. The comparisons between simulated and experimental data revealed good agreement and proved the validity of the developed process models.