Gallium Nitride (GaN) high electron mobility transistors (HEMTs) have garnered significant attention in micro/millimeter wave and terahertz technologies due to their unique material properties, including a wide bandgap, high charge density, high electron mobility, and high-temperature tolerance. To maintain fast evolution of communication toward terahertz frequencies, the key to HEMTs based on AlGaN/GaN heterojunction is the fabrication of nanoscale T-shape gates. Implementing a floating T-gate structure through electron beam lithography (EBL) has been explored to enhance the frequency performance of GaN HEMTs. But the fabrication of T-Gate through EBL is extremely inefficient and costly. A new technology has been developed based on the conventional 248 nm lithography machine and the self-developed resolution enhancement lithography technology assisted by chemical shrink (RELACS), so that traditional optical lithography could be used to manufacture T-gates with a L_g less than 100 nm, including floating T-gates. We believe that this technology would bring new revolution for the manufacture technology of T-gate structures in GaN HEMT devices.