[Edaily Reporter PARK MIN ] The KOSPI surged by over 6% on the 28th, marking its biggest rebound in three months. Amid a resurgence in artificial intelligence (AI) investment enthusiasm sparked by Anthropic’s initial public offering (IPO), SK hynix is seen to have fueled investor sentiment by announcing its first-ever quarterly revenue of 100 trillion won and an additional 60 trillion won in shareholder return measures. With investor sentiment returning, the KOSPI reclaimed the 6,000 mark for the first time in 10 trading days.

According to MP Doctor, the KOSPI index closed the regular session at 6,012.44, surging 374.10 points (6.63%) from the previous trading day. This marks the first time in three months—since July 31 (17.91%)—that the KOSPI has surged by more than 6% in a single day. The index soared to as high as 6,029.67 at one point during the session, maintaining strong upward momentum throughout the day, and settled back above the 6,000 mark on a closing basis for the first time in 10 trading days since October 14 (6,008.81).

At 9:54 a.m. that day, KOSPI 200 futures surged by more than 5% for one minute, triggering a buy-side sidecar in the KOSPI market. This marked the second consecutive day that a buy-side sidecar was triggered; the total number of sidecar activations on the stock market this year now stands at 54, comprising 27 buy-side and 27 sell-side triggers.

In terms of supply and demand, foreign and institutional investors drove the index higher with large-scale, coordinated buying. Foreign investors recorded net purchases of 780.4 billion won, while institutional investors recorded net purchases of 987.5 billion won, resulting in a combined net buying position exceeding 1.76 trillion won. In contrast, retail investors alone recorded net sales of 1.7758 trillion won amid the index’s rebound.

The main drivers behind the KOSPI’s rise that day were the top two semiconductor companies, including SK hynix, which announced its third-quarter earnings. SK hynix, buoyed by surging demand for High-Bandwidth Memory (HBM), achieved record-breaking quarterly revenue of 100 trillion won and operating profit in the 83 trillion won range for the first time, and announced an additional 60 trillion won shareholder return plan, completely turning the market sentiment around.

SK hynix’s third-quarter earnings exceeded market consensus by 7–9%, and its operating profit margin hit a record high of 79.7% for the quarter. Furthermore, the company confirmed plans to return a total of 100 trillion won to shareholders annually—including the 40 trillion won already spent on share buybacks—which strongly boosted investor sentiment.

On that day, SK hynix(000660)closed the regular trading session at 1,487,000 won, surging 10.89% from the previous trading day, while its intermediate holding company, SKSQUARE(402340), closed at 921,000 won, up 11.23%. Investor sentiment, which had been weighed down by concerns over the IPO of subsidiary Solidym and fears of an AI bubble, reversed instantly thanks to record-breaking earnings and shareholder-friendly policies.

SamsungElectronics(005930), which is set to announce its earnings on the 29th, also closed at 242,000 won, up 9.01%. SamsungElectronics(1P)(005935)also surged 11.10% to close at 190,100 won, while Samsung Life Insurance(032830)(8.82%), SamsungElectroMechanics(009150)(8.74%), KB Financial Group(105560)(4.34%), HyundaiMotor(005380)(1.89%), and LG Energy Solution(373220)(1.83%) all posted gains across the board.

On the same day, the KOSDAQ index also closed at 771.28, surging 27.45 points (3.69%) from the previous trading day. In the KOSDAQ market, institutional investors made net purchases of 128.5 billion won, while retail investors made net purchases of 38.8 billion won; foreign investors, meanwhile, made net sales of 160.5 billion won.

Buoyed by the rally of the two leading semiconductor companies, semiconductor materials, parts, and equipment stocks in the KOSDAQ market also rose in tandem. SIMMTECH Co., Ltd.(222800)(8.79%), JUSUNG ENGINEERING Co.,Ltd.(036930)(6.12%), WONIK IPS Co.,Ltd.(240810)(6.08%), EO Technics Co., Ltd.(039030)(5.95%), and LEENO Industrial Inc(058470)(3.42%) all surged, while ECOPRO CO., LTD(086520)(3.09%), ECOPRO BM CO., LTD.(247540)(3.07%), Alteogen Inc.(196170)(2.06%), and HLB INC.(028300)(1.88%)—all major secondary battery and biotech stocks—also posted solid gains.

In the securities industry, analysts assessed that while investor sentiment had been revived by Anthropic’s push for an IPO, SK hynix’s strong earnings report today served as an opportunity to dispel market doubts regarding the sustainability of AI infrastructure investment and memory demand.

Lee Jae-won, an analyst at Yuanta Securities Korea, stated, “Yesterday, Anthropic’s S-1 filing demonstrated the potential for monetizing AI services, and today, SK hynix proved that this demand is translating into memory prices, operating profits, and shareholder returns.” He added, “This is a process of overcoming a critical hurdle, where concerns about the sustainability of AI investment and theories that memory profits have peaked are being refuted by actual results.”

However, he advised that to solidify a sustained upward trend following this short-term sharp rebound, the market would need to be supported by continued foreign capital inflows and verified earnings from Big Tech companies.

Yang Hyun-kyung, an analyst at iM Securities, noted, “SamsungElectronics has also announced a cash dividend of approximately 30 trillion won for the third quarter as part of its 90 trillion to 110 trillion won shareholder return plan for this year.” She pointed out, “However, as seen in Meta’s expanded fundraising efforts, the market continues to scrutinize the funding sources for AI investments, so it is difficult to be optimistic about a sustained rebound based solely on expectations for shareholder returns.”

Researcher Lee Jae-won stated, “The cash flow and funding burdens of AI clients remain key variables to be verified,” adding, “The earnings reports from Microsoft (MS) and Alphabet, scheduled for release early this morning, along with SamsungElectronics’ announcement of its shareholder return policy this morning, will serve as a process to confirm the continuity of foreign investors’ net spot buying and their confidence in the profitability of AI investments.”