KOSPI Plunges 7.57%: Interest Rates Pull the Trigger, AI Profit Doubts Deepen the Fall

Circuit-breakers were triggered simultaneously on the KOSPI and KOSDAQ. Samsung Electronics and SK Hynix, down roughly 21% in seven trading sessions, have fallen to forward price-to-earnings ratios of around three times. The critical question is whether this constitutes an oversold condition or the early stages of a downward revision to profit forecasts.

The story in three lines

The KOSPI (South Korea's main stock exchange index) closed down 7.57% at 5,554.22; the KOSDAQ fell 7.65%. Automatic selling halts and circuit-breakers were triggered on both markets. The KOSPI has now shed roughly 21% in seven trading sessions.

The immediate trigger was America's September consumer-price index, which came in at 3.7% year-on-year against an expected 3.6%, stoking fears of further Federal Reserve rate rises. The deeper driver of the sell-off was mounting scepticism about the returns on artificial-intelligence investment; heavy concentration in Samsung Electronics and SK Hynix, combined with sustained foreign selling, amplified the decline. Concerns about China's CXMT memory chipmaker were a secondary factor.

Based on today's closing prices, Samsung Electronics and SK Hynix trade at forward price-to-earnings ratios of approximately 3.2 times and 2.8 times respectively, and forward price-to-book ratios of approximately 1.3 times and 1.5 times. Valuations have priced in a substantial degree of earnings deterioration, but the risks of further estimate downgrades and additional price declines have not disappeared.

What happened in the market today

Approximately 71% of foreign net selling was concentrated in Samsung Electronics (roughly ₩1.46 trillion) and SK Hynix (roughly ₩1.11 trillion). Retail and institutional buyers absorbed close to ₩3 trillion, but it was not enough. Notably, foreign investors were net buyers of KOSPI 200 futures to the tune of ₩328.1 billion — turning to the buy side in derivatives even as they sold heavily in the cash market.

The KOSPI's closing price fell below its 30 July close of 5,593.56. A little over a week ago, the index stood at roughly 7,004.

The trigger and the amplifiers: disaggregating the causes

The causes are distinct in nature. Lumping them together obscures more than it reveals.

Interest rates: the trigger. America's September CPI rose 3.7% year-on-year, exceeding market expectations of 3.6%. Fears that the Federal Reserve might raise rates further sent the Nasdaq down 1.88%, the S&P 500 down 1.11%, and the Philadelphia Semiconductor Index down 4.3% on 14 October (US time). Higher interest rates raise the discount rate applied to distant future earnings, and growth stocks and semiconductors tend to suffer the most.

Doubts about AI investment returns: the main driver of the severity of the decline. Selling was concentrated in semiconductor stocks, and markets with heavy semiconductor weightings were hit hardest. TSMC announced on the same day that its third-quarter net profit surged approximately 69% to an all-time high — yet sentiment remained unmoved. What markets are questioning now is not current performance but sustainability. Gartner estimates AI infrastructure investment will reach roughly $1 trillion this year, with a further $6 trillion to follow between 2027 and 2030. In a high interest-rate environment, the question is how quickly that enormous outlay can generate a return. Interest rates and AI scepticism are not independent variables: the higher rates go, the higher the bar for justifying investment. The Nikkei's first wave of selling in July was similarly attributed to concerns about the durability of the AI rally.

Positioning and flows: the amplifier. Foreign investors sold more than ₩21 trillion worth of Korean equities over eight trading sessions. The concentration of that selling in Samsung Electronics and SK Hynix compounded the index's decline.

CXMT: a secondary factor. Concerns that capacity expansion by China's CXMT could weigh on commodity DRAM prices have been cited. When CXMT's parent company listed on 27 July, those concerns did serve as an actual sell trigger. Today, however, interest rates and AI scepticism appear to have been far more significant; CXMT's role seems limited to unsettling sentiment around the supply outlook.

Why South Korea is hit harder

The answer lies in concentration. At end-June, Samsung Electronics and SK Hynix together accounted for more than 50% of the KOSPI's market capitalisation, and 60.7% of the KOSPI 200 (figures compiled by Meritz Securities, reported 28 July). The index effectively moves with these two stocks. As of 28 July, the semiconductor sector explained 80.2% of the KOSPI's decline from its peak. The rotation into other stocks that might otherwise cushion a sell-off in the market's leading names was notably absent this time.

Layered on top of this concentration is a structural flows problem. During the sharp falls of June and July, mechanically triggered selling by single-stock leveraged exchange-traded funds was identified as a key culprit. The financial regulator's decision on 31 July to raise the minimum cash deposit for such products to ₩30 million changed the picture. Trading volumes in the 16 relevant ETFs fell from ₩12.4485 trillion on 30 July (32.5% of total KOSPI turnover) to ₩919.9 billion on 5 August (3.65%). It is therefore difficult to attribute today's losses primarily to a repeat of July's ETF-driven cascade. The supply-and-demand forces now roiling the market fall into three categories.

Foreign investors: the market from which rebalancing flows exit first. Samsung Electronics and SK Hynix, by virtue of their trading liquidity, are among the easiest positions for global funds to exit in size over a short period when cutting country or sector exposure. Foreign investors directed 71% of their net selling today into these two stocks. Analysis by Meritz Securities noted that at the half-year end on 26 June, funds with mandatory risk-limit and country-weighting requirements were offloading Korean semiconductor baskets from the opening auction. An analyst at LS Securities argued that foreign net selling of ₩152 trillion of KOSPI equities through 6 July was better characterised as profit-taking and target-weight rebalancing than as an outright exit. Some in the market also point to the combined effect of South Korea's continued exclusion from the MSCI Developed Markets index and global fund rebalancing flows. If this is rebalancing rather than flight, selling pressure may ease once positions are adjusted — but the timing is impossible to predict.

Institutional investors: automatic selling constrained by risk limits and target weightings. Institutional selling reflects less individual conviction than the mechanical stop-loss and position-reduction orders that kick in when volatility breaches risk limits. On 26 June, foreign and institutional investors sold a net ₩4.3 trillion and ₩4.1 trillion respectively. One analysis noted that the National Pension Service's target domestic-equity weighting is 20.8%, yet its actual weighting reached 27.7% at end-Q2, with Samsung Electronics and SK Hynix accounting for 55.5% of its domestic equity portfolio. The implication is that persistent selling pressure exists simply to bring the portfolio back to target. Goldman Sachs cited the simultaneous rebalancing of seven semiconductor ETFs (with combined assets of roughly ₩19 trillion) and options expiries as sources of short-term selling pressure earlier in October. It should be noted, however, that institutional investors in aggregate were net buyers of approximately ₩1.7 trillion on the KOSPI today. The breakdown by type of institution is not yet available; whether any mechanical selling occurred within that aggregate will only become clear when detailed flow data are released.

Retail investors: margin-financed positions being unwound. Margin loan balances on the KOSPI fell from a 2024 peak of ₩38.6 trillion on 24 June to ₩28.9350 trillion on 31 July — a reduction of roughly ₩10 trillion — with forced liquidations of approximately ₩1 trillion occurring during July. Much of the leverage has already been cleared, so forced selling may be smaller in scale than in July. Nevertheless, as of early July, margin balances in Samsung Electronics and SK Hynix combined stood at ₩10.6 trillion, accounting for roughly 36% of total KOSPI margin balances. If share prices fall further, collateral ratios will break and forced liquidations could again put downward pressure on prices. Today's forced-liquidation volumes and the latest margin balance data were not available at the time of writing.

This kind of sharp decline is not new this year. As of reporting on 23 July, automatic selling halts on the KOSPI had been triggered 40 times in 2024 — a record, surpassing the previous high of 26 in 2008. On 28 July, the KOSPI closed down 10.84% at 6,023.66; the following day it fell a further 5.98%, with an intraday decline exceeding 12%. Today's drop is not the largest of the year; it is one of several severe sell-offs in what has become a recurring pattern.

What the price is saying: a check on forward valuations

The calculations below apply 12-month forward earnings-per-share and book-value-per-share figures derived from consensus estimates (FnGuide, MarketScreener) to today's closing prices. The forward EPS and BPS figures are as of 12 October and therefore incorporate third-quarter preliminary results, but not any revisions made following today's decline.

SK Hynix's 2027 EPS and BPS are not directly verified figures but have been back-calculated or estimated from market data. The margin of error is approximately ±1% for EPS and ±5% for BPS, so the forward P/B should be treated as a range of roughly 1.4 to 1.6 times.

How expensive do the stocks look if earnings fall? Examining how P/E ratios rise as forward EPS declines gives a sense of how much is already priced in at current levels.

Even if earnings were cut in half, P/E ratios would still be in the mid-single digits. On current consensus, SK Hynix would recoup its entire market capitalisation through net profit alone in less than three years. On an earnings basis alone, it is reasonable to argue that current prices reflect a large part of a bear-case scenario.

What does the P/B ratio imply about market assumptions? Price-to-book is a function of sustainable return on equity (ROE) and the required rate of return. Using a simple Gordon Growth Model with a 10% required return and 3% growth, a forward P/B of 1.3 times implies a long-run ROE of roughly 12%; 1.5 times implies roughly 13%. Widening the assumptions to a 9–11% required return and 2–3% growth yields a range of 11–15%. By contrast, the consensus forward ROE (forward EPS divided by forward BPS) is approximately 42% for Samsung Electronics and 52% for SK Hynix. In other words, today's price implies that these exceptionally high returns will revert to more normal levels before long. This is a simplified model sensitive to its assumptions; it should be read as a tool for understanding market expectations, not as a definitive answer.

Implied price targets from historical P/B multiples. Applying various multiples to the same forward BPS figures produces the following:

Two reference points are worth noting. Samsung Electronics fell to a P/B ratio of 0.98 times in November 2024, when its share price touched ₩55,000 — below liquidation value. In the other direction, Kyobo Securities (in a February research note) put Samsung Electronics' fair P/B at 2.7 times and SK Hynix's at 4.08 times on the basis of ROE, describing the latter as well above any historical high. These two benchmarks are not directly comparable, since the historical trough is calculated on a trailing basis, while the multiples in the table are applied to forward BPS. Forward BPS already includes future earnings yet to be realised, so the same multiple will yield a higher absolute price.

The bull case. As of 12 October, consensus estimates remain on an upward trajectory through next year. Samsung Electronics' 2027 EPS estimate has been revised up from ₩67,653 to ₩72,140; SK Hynix's 2026 EPS estimate has also been nudged higher. A scenario in which volume growth offsets price declines, leaving earnings broadly intact, cannot be ruled out. In that case, today's sell-off reflects doubt rather than deteriorating fundamentals.

Risks to watch.

Consensus figures pre-date today's fall. If downgrades follow, P/E ratios will be higher than the figures shown here.

Samsung Electronics' 2026 EPS estimate was actually revised downward — from ₩47,816 to ₩45,419. The reason is not known. An "upward revision to earnings" does not apply uniformly across all years.

Forward BPS only accumulates if earnings are actually delivered. A low forward P/B is not an entirely independent argument from a low forward P/E.

Memory chips are a cyclical industry. In past downturns, earnings did not merely halve — they collapsed. In such scenarios, P/E ratios can actually soar even as share prices fall, eliminating any apparent "cheapness."

Undervaluation does not signal a floor. Prices can fall further still.

A framework for individual investors

The following is offered as a decision-making framework, not as investment advice. Any investment decisions and their consequences remain the responsibility of the individual investor.

The case against panic selling. Selling in a panic after a 20–30% decline in a week locks in losses. As the analysis above suggests, current prices appear to have priced in a substantial portion of a bear-case scenario. That said, investors holding margin-financed positions may face forced liquidation and lose the ability to choose. In such cases, maintaining collateral ratios takes priority over views on valuation.

If you have cash available. One approach is to set a maximum position size and a time horizon, then deploy funds gradually rather than all at once. Staged buying reduces exposure to both further declines and premature commitment ahead of a recovery.

If cash is limited. Waiting for signs that a bottom has formed is another option. Indicators to watch include: a reversal lower in the VKOSPI volatility index; a slowdown in foreign net selling; stabilisation of the won/dollar exchange rate; a change in US rate expectations; and evidence that margin-forced selling has run its course. These signals may not all appear simultaneously.

Check your concentration. It is worth reviewing how much of your portfolio is in Samsung Electronics and SK Hynix, and whether you could withstand a further 30% decline in either stock.

A cautionary precedent. After the KOSPI closed at 5,593.56 on 30 July (with an intraday low of 5,262.77 on 29 July), the index rebounded roughly 25% to recover the 7,000 level. Today it has closed below that 30 July level again. A low that appeared to hold once may be tested again — and again.

Did the founders' share purchases offer any protection?

Two controlling shareholders purchased shares before today's sell-off; both purchases are now showing paper losses. Lee Jae-yong, chairman of Samsung Electronics, bought 7,667,100 Samsung shares on 12 October from Hong Ra-hee (Honorary Director of Leeum Museum of Art) at ₩250,500 per share. Compared with today's closing price of ₩210,000, that represents a loss of approximately 16%, or a paper loss of roughly ₩31 billion. An additional 11,158,000 shares are due to be transferred to him by 12 November; at today's closing price, those shares are worth approximately ₩2.34 trillion. Chey Tae-won, chairman of SK Group, bought 3,620 SK Hynix shares on 30 July at roughly ₩1,320,000; today's closing price is about 4.5% below that level. Both are simple comparisons — the gap between purchase price and today's closing price does not, in itself, measure investment performance. And even insider buying, however significant as a signal, proved unable to stem the tide of short-term selling pressure.

What to watch next

US inflation and the rate path. The variable that pulled today's trigger — America's CPI — will be the most direct influence on the next round of data releases and central bank communications.

Foreign investor flows. Whether the pattern of futures buying alongside cash selling continues, and whether the won/dollar rate (₩1,344.6) stabilises.

Consensus estimate revisions. Whether the EPS forecasts as of 12 October are revised downward. Both P/E and P/B analysis hinges on these numbers.

Unwinding of margin positions. Margin loan balances and forced-liquidation volumes for Samsung Electronics and SK Hynix; and any policy response from the government or financial regulators.

Samsung Electronics' third-quarter dividend record date. The per-share dividend and total payout are expected to be confirmed at the October board meeting.