Korea's AI trade snaps: Kospi plunges 8% with circuit breakers as SK hynix, Samsung drop 10%+, same day TSMC posts record quarter

What's the deal? South Korea's benchmark Kospi tumbled 8.13% to 5,515.76 on Thursday, as Samsung ElectronicsDealroom has a profile for this one. Try Dealroom → and SK hynixDealroom has a profile for this one. Try Dealroom → both fell more than 10%, triggering circuit breakers on both the Kospi and the tech-heavy Kosdaq — the first time both markets had activated circuit breakers on the same day since 29 July.

The details: SK hynix sank 11.35% to US$1.06K, pushing its market capitalisation below the US$838.4B threshold to US$779B. Samsung Electronics plunged 10.13% to US$174.8. Samsung Electro-MechanicsDealroom has a profile for this one. Try Dealroom → dropped 16.81% and SK SquareDealroom has a profile for this one. Try Dealroom → shed 10.45%.

How bad is the slide? It's not a one-day event. The Kospi is down more than 16% over the past month and more than 40% from the record high of 9,385.59 it hit in June — its lowest close in about six months, and a seventh straight losing session, the longest losing streak since September 2024. The proximate trigger was hotter-than-expected US inflation data (September CPI +3.7% year-on-year) reviving fears of further rate hikes, on top of growing doubts about the durability of AI-linked capital spending.

The split screen: The same day, Taiwan's TSMC posted a record third-quarter net profit of US$22.1B ($46.36 billion in revenue), up 68.7% year-on-year — its sixth straight record quarter, beating analyst estimates and guiding Q4 revenue up another 14% sequentially on relentless AI-chip demand.

The signal: One AI winner books records while Korea's memory giants crater on the same news cycle — a sharp reminder that AI-driven demand for memory and AI financing fears can hit the same supply chain very differently depending on where in it you sit.

Read more: The Korea Herald · CNBC

Image credit: walknboston