As the main-stream technology to fabricate the deep-submicron T-gates of high-frequency GaN HEMT(High Electron Mobility Transistor) in industry, electron beam lithography faces the problems of low efficiency, insufficient yield, and high cost. In this paper, an 80 nm T-gate GaN HEMT with pure optical exposure has been successfully manufactured for the first time on a 6-inch industrial production line using integrated side wall technology, and the performance parameters of the device are comprehensively characterized and analyzed. The device displays a maximum output current per unit (millimeter) gate width of 993 mA, a peak transconductance of per unit (millimeter) gate width 385 mS, a threshold voltage of -3.25 V, an off-state breakdown voltage exceeding 80 V, and a f_T/f_max of 64/175 GHz. When operated at 28 V, the saturated output power, the associated power gain, and the power added efficiency of the device at 16 GHz are 26.95 dBm(4.9 W per millimeter), 11.08 dB, and 49.78% respectively; while at 30 GHz, these data are 26.15 dBm(4.1 W per millimeter), 8.8 dB, and 44% respectively. The results show that the integrated sidewall technology has a good application prospect in deep-submicron GaN HEMT manufacturing.