Yonhap reported on 28 October 2026 that the KOSPI gained 374.1 points, or 6.63%, to close at 6,012.44, after rising as high as 6,032.28 during the session. Yonhap said the rally was led by chipmakers after SK hynix reported record quarterly earnings and announced additional shareholder returns. Yonhap said SK hynix posted record-high third-quarter revenue and operating profit.
SK hynix rose 10.89% to 1.49 million won and Samsung Electronics rose 9.01% to 242,000 won, according to Yonhap. The 6,000 level held at the close, not only intraday.
Short explainer · AI memory brief
A vertical news Short narrated from the published headlines and opening lines of this piece and four related FourWeekMBA pieces on AI memory chips.
Business Pill · The memory wall
An evergreen Business Engineer explainer on why memory, not only compute, limits AI performance. It explains the general idea only and does not discuss the KOSPI or the companies in this piece.
The key insight: As we read it, the rally rewarded cash returned as well as profit: Yonhap tied it both to SK hynix’s record quarter and to a shareholder return program worth more than 100 trillion won for 2026.
Yonhap listed the chip-linked gains at the close: SK Square rose 11.23% to 921,000 won and Samsung Electro-Mechanics rose 8.74% to 1.3 million won, alongside SK hynix and Samsung Electronics.
Yonhap reported that the Korea Exchange activated a buy-side sidecar shortly before 11 a.m., suspending program trading buy orders for KOSPI-listed stocks for five minutes. Advancers outnumbered decliners 580 to 288, on volume of 223.2 million shares worth 19.83 trillion won.
Closing prices on 26 and 28 October 2026, indexed to 26 Oct = 100: SK hynix 1.28M to 1.49M won, Samsung Electronics 213,000 to 242,000 won, KOSPI 5,469.47 to 6,012.44. Two-session percentages are our arithmetic from Yonhap closing reports; on 28 Oct alone Yonhap reported SK hynix +10.89%, Samsung +9.01%, KOSPI +6.63%. The KOSPI’s intraday high on 28 Oct was 6,032.28; the chart uses closes only.
What Was Posted on X
$MU is up as much as $32 overnight after SK Hynix reported earnings.
At the same time, Kioxia is up more than 10% in Japan and Samsung is up about 7% in Korea.
When SK Hynix says it is sold out through 2029, investors immediately ask who else benefits, and the answer is every major memory maker.
Micron sells into the exact same shortage, with the same AI customers fighting for supply.
The whole memory group is moving together tonight.
Milk Road AI posted on 28 October that Micron was up as much as $32 overnight after SK hynix reported earnings, with Kioxia up more than 10% in Japan and Samsung up about 7% in Korea. These are the poster’s figures.
Korean semiconductor stocks are looking RIDICULOUSLY undervalued right now.
According to Goldman Sachs, Koreaโs semiconductor sector is trading at just 2.8x forward earnings, the LOWEST valuation in more than 20 years. To put that into perspective, the historical average is around 10x earnings, meaning investors are paying less than a third of what they historically have for these companies. And whatโs crazy is that this is happening during one of the biggest memory supercycles weโve ever seen. The market is essentially pricing in a major decline in future earnings because investors donโt believe todayโs memory prices and profit margins are sustainable.
During its latest earnings call, SK Hynix said its DRAM and HBM supply is effectively sold out through 2029, with HBM demand more than DOUBLE what it can currently supply. Management also expects memory shortages to persist through 2030. And even SK Hynix believes its stock is undervalued. The company announced plans to return approximately $75 billion to shareholders this year, including more than $45 billion through share buybacks and cancellations. Management believes its share price doesnโt reflect the earnings and cash flow the business is generating, and plans to continue repurchasing shares every quarter.
Now, memory has always been a cyclical business, and thereโs no guarantee these elevated margins will last forever. But I think the market is underestimating just how long this cycle could last. If you want to see how Iโm investing around the memory supercycle, check out my full portfolio below.
An X user posted that, according to Goldman Sachs, Korea’s semiconductor sector trades at 2.8 times forward earnings, which the poster calls the lowest valuation in more than 20 years, against a historical average the poster puts at around 10 times.
Why Yonhap Says It Rallied
One-day change at the 28 October 2026 close: SK hynix +10.89%, Samsung Electronics +9.01%, KOSPI +6.63% to 6,012.44 (intraday high 6,032.28). Source: Yonhap closing report.
Yonhap tied the move to SK hynix’s results and to a shareholder return program it said is worth more than 100 trillion won (US$75.3 billion) for 2026.
Lee Jae-won of Yuanta Securities told Yonhap: “SK hynix demonstrated that strong demand for AI chips can translate into solid operating profits and shareholder returns, easing concerns about the sustainability of the AI-driven rally and a potential peak in the memory chip cycle.”
Yonhap reported that foreigners bought a net 815.83 billion won of shares and institutions a net 960.79 billion won, while individuals sold a net 1.8 trillion won.
Two Sessions, Not One
The jump built on the day before. On 27 October, Yonhap reported, the KOSPI rose 3.09% to 5,638.34, with SK hynix up 5.18% to 1.34 million won and Samsung Electronics up 4.23% to 222,000 won. On 26 October the index had closed down 1.46% at 5,469.47, with SK hynix at 1.28 million won and Samsung at 213,000 won.
By our arithmetic from those Yonhap closes, SK hynix is up about 16.4% over the two sessions, Samsung Electronics about 13.6% and the KOSPI about 9.9%.
As we read it, the gains ran across the chip names: Yonhap lists SK Square, the parent of SK hynix, up 11.23% and Samsung Electro-Mechanics up 8.74%, alongside SK hynix and Samsung Electronics.
Lee Jae-won of Yuanta Securities told Yonhap the results eased concerns about the sustainability of the AI-driven rally and a potential peak in the memory chip cycle.
Yonhap said foreigners bought a net 815.83 billion won of shares and institutions a net 960.79 billion won, while individuals sold a net 1.8 trillion won.
Lee Jae-won, Yuanta Securities, to Yonhap, 28 October 2026
“SK hynix demonstrated that strong demand for AI chips can translate into solid operating profits and shareholder returns”
Three Implications
FOR SK HYNIX Yonhap reported a shareholder return program worth more than 100 trillion won (US$75.3 billion) for 2026, announced with record-high third-quarter revenue and operating profit.
FOR SAMSUNG ELECTRONICS Yonhap reported Samsung Electronics up 9.01% to 242,000 won on 28 October, after a 4.23% rise to 222,000 won the session before.
FOR THE KOSPI Yonhap reported that the Korea Exchange activated a buy-side sidecar for the second straight session; it is triggered when KOSPI 200 futures rise at least 5% and stay there for at least one minute.
The framework argues that the binding constraint on AI scaling has shifted to High Bandwidth Memory, and puts it plainly: “Memory is becoming the new compute.”
Yonhap reports that the KOSPI closed above 6,000 in a rally led by chipmakers after SK hynix’s record quarter. The framework was published in December 2025 and does not discuss this rally.
What Is Not Established
Yonhap’s report does not say whether 6,012.44 is a record close for the KOSPI, so we do not call it one. Some Korean outlets described the move as a return above 6,000; we did not read those reports in full.
A relay of Japanese trading put Kioxia up about 14% in Tokyo on the same day; we have not confirmed a closing figure from a primary or trusted source, so it is not part of the chart.
This Week In The AI Supercycle
Execution Fault Lines, Concentrated Demand, and Geopolitical Firewalls
This week’s issue: the AI build is not short of demand for its parts. It is short of cheap money, and its end revenue rests on a narrow base of large, often venture-funded buyers.
Yonhap reports that the KOSPI closed at 6,012.44 on 28 October, up 6.63%, led by chipmakers after SK hynix’s record quarter and a shareholder return program of more than 100 trillion won, with SK hynix up 10.89% and Samsung Electronics up 9.01%.
A note on sourcing. Every closing price, percentage move, flow figure and the Yuanta quote come from Yonhap’s closing reports for 26, 27 and 28 October 2026. The cause of the rally is given as Yonhap states it. Two-session changes and the indexed chart are our arithmetic from those closes. The KOSPI’s intraday high of 6,032.28 is shown separately from the 6,012.44 close.
Gennaro Cuofano is a CRO and tech executive who has worked in AI since late 2015, starting with bringing NLP, natural-language generation, voice and chatbot products to the marketing industry. His background is in law and finance: he holds a Master's degree in Law and an International MBA with an emphasis on corporate finance (LUISS Business School and the University of San Diego, 2012), and worked as a financial analyst at a real-estate investment firm in San Diego and as an assistant controller. His work focuses on business model strategy, business engineering and, more broadly, structural analysis: how companies make money, read from their own filings. He created FourWeekMBA and leads research there and at The Business Engineer, his newsletter on AI and business strategy, with over 95,000 subscribers and more than 1,000 published analyses. His writing has also appeared on Entrepreneur (for example, How to Digitize a Family Business in Europe) and HackerNoon. Find him on LinkedIn and Substack. See how we source.
