Guide · Markets
DRAM, NAND and HBM: Why Memory Chip Stocks Swing Harder Than the Rest of Tech
Samsung, SK Hynix and Micron make the memory inside every phone, PC and AI server. Here's how the memory business works, why high-bandwidth memory changed it, and why a rumour about a Chinese rival can move a whole national stock market.
Every computer needs two kinds of memory. DRAM is the fast, temporary working memory that holds what a processor is using right now; it forgets everything when the power goes off. NAND flash is the slower, permanent storage inside solid-state drives and phones. Both are made in enormous volumes, and for most of their history they have behaved like commodities: chips from different makers are largely interchangeable, so price is set by supply and demand.
Three companies dominate DRAM: Samsung Electronics and SK Hynix in South Korea and Micron in the US. That concentration, combined with the commodity nature of the product, creates a famous boom-and-bust cycle. When demand is strong, prices rise, profits soar and the makers invest in new factories. Two or three years later, those factories add supply just as demand cools, prices collapse, and profits can turn into losses within a few quarters. Memory stocks often move a year or more ahead of the earnings, as investors try to anticipate the turn.
High-bandwidth memory, or HBM, changed the picture. AI accelerators need to feed huge amounts of data to their processors very quickly, so HBM stacks several DRAM chips vertically and connects them with thousands of tiny channels. It is much harder to make than ordinary DRAM, sells for far higher prices, and is often sold under long contracts with a few big customers. For SK Hynix in particular, HBM became a major source of profit, and investors started valuing memory makers more like AI companies than commodity producers.
That shift is also what makes the group fragile. If investors start to doubt AI spending, memory makers lose the premium they gained from it. And because ordinary DRAM is still a commodity, any sign of new competition matters. In October 2026, reports that China's CXMT had made progress on denser memory chips — together with renewed doubts about AI spending — helped send SK Hynix down more than 10% and Samsung about 8% in a single session, while Micron fell below $1,000 for the first time since mid-September. South Korea's Kospi, heavily weighted toward those two stocks, lost 14% in five sessions.
For traders, a few habits help. Watch memory prices and the makers' guidance rather than only headline earnings, because the cycle turns on prices. Pay attention to capacity announcements, since new factories are tomorrow's supply. Remember that Samsung and SK Hynix make up a large share of Korea's market, so trading the Kospi or Korean ETFs is partly a bet on memory. And expect memory stocks to move more than the broader semiconductor index, in both directions.