A nanofabrication technology providing device isolation at an active pitch of 300 nm has been developed using x‐ray lithography for pattern definition. The isolation scheme uses oxide filled trenches etched into the silicon substrate, which are 300–350 nm deep and have a 150 nm minimum width. Chemical mechanical polishing is utilized to achieve global planarization. The superior diode leakage and gate oxide (tox=55 Å) performance, excellent metal–oxide–semiconductor field effect transistor characteristics, and robust latch‐up behavior demonstrated by this trench isolation technology, present it as a key enabler for continued scaling of semiconductor technologies. The experimental data presented predicts that with careful attention to process integration, trench isolation can be scaled well into the sub‐0.25 μm size scale.