China's push into high-end AI memory has hit a wall, which is bad news for Beijing's chip ambitions and good news for Samsung, SK Hynix, and Micron.

• Chinese memory maker CXMT is getting only 25-30% usable chips from its 8-layer HBM3 production.
• Out of every 100 chips made, 80 fail quality checks — and even the survivors lose more in final testing.
• The problem is the hardest part of the process: drilling thousands of tiny vertical holes through each chip and bonding the layers together.
• CXMT grew fast because the big Korean and US makers shifted capacity to HBM, leaving it room to sell ordinary DRAM.
• HBM is now the key bottleneck in the AI chip supply chain as data centers keep expanding.

Outlook: The established memory giants keep their grip on AI memory for now, with China years away from catching up.