South Korea's KOSPI index plunged 11.4% intraday on July 29, 2026, to 5339.56 points, according to CNA, extending a slide from a 6.1% morning drop after already falling nearly 11% the prior session, per CNA and SETN. SK Hynix (SK海力士) sank as much as 18% and Samsung Electronics (三星電子) fell 12.5%, per CNA, while SETN reported the July 28 rout triggered South Korea's 10th circuit breaker of the year and dragged Taiwan's memory stocks to limit-down.
How large was the KOSPI plunge, and how fast did it unfold?
The sell-off in South Korea's benchmark KOSPI index (韓國綜合股價指數) unfolded over two trading sessions with escalating losses. According to CNA, the index had already tumbled nearly 11% on July 28, and selling pressure continued to build into the next session. CNA reported that on the morning of July 29, KOSPI was down 6.1%, trading at 5656.65 points — but by later in the same session, CNA reported the decline had deepened to 11.4%, with the index at 5339.56 points.
The acceleration traces back to July 28, when SETN (stock.setn.com) reported KOSPI plunged more than 8% intraday, triggering South Korea's 10th circuit breaker of the year. That breaker event came one day after SK Hynix's (SK海力士) US-listed ADR had already turned lower on July 27, closing at $143.02 — below its $149 IPO price, per SETN.
| Timepoint | KOSPI move | Source |
|---|
| Jul 27 (SK Hynix ADR, US) | ADR closes at $143.02, below $149 IPO price | SETN |
| Jul 28 (intraday) | Plunges over 8%, triggers 10th circuit breaker of the year | SETN |
| Jul 28 (session close, as reported Jul 29) | Down nearly 11% | CNA |
| Jul 29 (morning) | Down 6.1%, at 5656.65 points | CNA |
| Jul 29 (later intraday) | Down 11.4%, at 5339.56 points | CNA |
Which tech stocks led the decline, and by how much?
Memory-chip makers SK Hynix and Samsung Electronics (三星電子) were the two biggest drags, and their losses widened as the session progressed — mirroring the index's own acceleration. CNA reported that in the morning of July 29, SK Hynix was down 10% and Samsung Electronics had fallen more than 6%; by later in the session, CNA reported SK Hynix's decline had widened to 18% while Samsung Electronics fell 12.5%.
SETN's account of the prior day, July 28, described the same two stocks as the session's biggest losers: SK Hynix plunged more than 11% and Samsung Electronics dropped about 9%, with SETN noting the "memory duo" (記憶體雙雄) were first to be hit.
| Stock | Jul 28 intraday (SETN) | Jul 29 morning (CNA) | Jul 29 later intraday (CNA) |
|---|
| SK Hynix (SK海力士) | -11%+ | -10% | -18% |
| Samsung Electronics (三星電子) | ~-9% | >-6% | -12.5% |
How did Taiwan's market react to the Korean rout?
The pressure crossed the strait on July 28. SETN reported that Taiwan's memory-chip group weakened in tandem with the Korean sell-off, with Nanya Technology (南亞科), Winbond (華邦電), and Macronix (旺宏) all hitting daily limit-down during the session. SETN's report ties the moves directly to the same-day Korean rout — the only evidence in this pack that speaks to Taiwan's market reaction, and it involves three named issuers moving to the maximum allowable daily decline simultaneously.
What were the main drivers behind the sell-off?
Two distinct factors are documented as being in play around the same period. First, SETN reported that The Wall Street Journal had disclosed NVIDIA (輝達) may provide roughly $250 billion in financing guarantees to help OpenAI lease large-scale AI data-center computing capacity — a report that, per SETN, fueled market concern over "circular financing" (循環融資) risk in the AI sector and coincided with a near-5% drop in NVIDIA's own share price on July 28.
Second, SETN reported a regulatory change from South Korea's Financial Services Commission (FSC, 韓國金融服務委員會): new oversight measures for single-stock leveraged ETFs and ETNs were moved up to take effect July 31, raising the minimum cash margin threshold for retail investors trading these products from 10 million won to 30 million won.
What this means
The evidence shows a compounding pattern rather than a single-day shock: CNA's and SETN's numbers line up to show KOSPI's decline widening from roughly 6% to 8%, then to nearly 11%, and finally 11.4% across just two sessions, with SK Hynix and Samsung Electronics falling in the same escalating sequence each time. SETN's reporting places two distinct triggers inside that same window — the NVIDIA-OpenAI financing-guarantee report that dented NVIDIA's own stock, and the FSC's tightened margin rules for leveraged ETF/ETN trading due July 31 — without establishing which, if either, directly caused the circuit-breaker-triggering drop on July 28. What the evidence does confirm is that the shock did not stay contained to Seoul: SETN's report of Nanya Technology, Winbond, and Macronix all hitting limit-down in Taiwan on the same day shows the memory-sector sell-off moved across markets within a single trading session.