An AI accelerator is useless without high-bandwidth memory stacked beside it, and SK hynix took 63.2% of HBM revenue in 2025. Samsung and Micron split most of the rest. Korea ranks #1 on the Memory control basis as a direct result.
HBM carries a substitutability weight of 0.95 here, near the top of the scale, because qualifying a memory vendor with an accelerator designer takes years. A customer cannot switch HBM supplier the way it reorders commodity DRAM. Supply gates GPU output directly, which is why HBM allocation, not wafer starts, has been the binding constraint on accelerator shipments.
The financial evidence is unambiguous. SK hynix closed 2025 with ₩97.15tn of revenue and ₩47.21tn of operating profit — a 49% margin — and overtook Samsung on annual profit for the first time in its history. When a bottleneck is real, it shows up in the margin.