T-shaped gate formation is a important process step in the fabrication of high frequency monolithic microwave integrated circuits (MMIC), many different lithography process have been used for this purpose, such as bi-layer or tri-layer using e-beam lithography, hybrid UV-e-beam lithography. Proximity x-ray lithography (PXL) has shown many advantages in the MMIC manufacturing, such as high resolution, large process windows, low cost and high throughout, and so on. In this article, a new ZEP520/P(MMA-MAA)/ZEP520 tri-layer process using synchrotron-based PXL is proposed for the T-shaped gate formation, without any additional intermediate layer, the resists intermixing problem has been solved successfully, a dark-field isolated trench x-ray mask was used for this purpose. A three stage development process using xylene for the head, MIBK:IPA=1:3 for the middle and xylene for the foot was also used. Initial work has shown this process to be robust.