Foreigners Sold Samsung and SK Hynix, the KOSPI Rallied Anyway

Foreign investors sold Samsung Electronics and SK Hynix heavily on Thursday morning, yet the KOSPI still closed up 1.95% at 6,971.35. That gap between who was selling and what went up is the single most informative detail of the October 1 session, and it is the only thing this post is about. The daily wrap-up covers the full tape; here we take apart one question: if foreigners and retail investors were both net sellers of the KOSPI, who actually paid for the rally, and how durable is a rally financed that way?

The flow picture the headline hides

The closing flow data on the KOSPI reads like a down day. Foreigners finished as net sellers of 597.2 billion won. Individuals were far bigger net sellers at 1.234 trillion won, which the source data attributes to likely profit-taking. The only net buyer among the three groups was the institutional side, at 305.6 billion won. On a naive reading, 305.6 billion won of institutional buying is a small number to set against roughly 1.8 trillion won of combined selling — and yet the index added 133.31 points.

The resolution of that puzzle is concentration. The morning selling was not spread across the market; per the session data, foreign selling was focused on Samsung Electronics (866.7 billion won) and SK Hynix (608.5 billion won), which together accounted for about 72% of total foreign net selling during that phase. When those same two names reversed in the afternoon — Samsung Electronics closing +2.79%, its preferred shares +4.76%, SK Hynix +3.21% — the index-level arithmetic flipped with them. In a market this top-heavy, the sign on two tickers can matter more than the sign on three investor groups.

One arithmetic detail is worth flagging without over-interpreting it: the full-day foreign net-sell figure of 597.2 billion won is considerably smaller than the morning selling in those two stocks alone. At minimum, that means the foreign selling did not continue at its morning intensity into the close. The source does not break down afternoon foreign flows by name, so we cannot say precisely where the moderation happened — only that it did.

Why the morning selling was rational

The foreign selling was not noise. The US 10-year Treasury yield traded in the 5.3% range intraday, its highest level since May 2002, with the 30-year above 5.6%. Long rates at multi-decade highs are a direct valuation headwind for long-duration growth assets, and large-cap memory stocks are exactly that. The won also weakened, with USD/KRW rising 0.61% to 1,358.78 — a softer won is consistent with the pressure a foreign holder of Korean equities was feeling on Thursday morning. The KOSPI opened at 6,814.49, down 0.34%, and slid further toward the 6,780 area before anything changed.

What flipped the tape — and why it outranked rates

The reversal came from earnings, not macro. Micron Technology's overnight results beat market expectations on both revenue and EPS, and its next-quarter revenue guidance of around $61.5 billion came in well above a consensus in the $57 billion range. Layered on top was the report that 2026 HBM volumes are fully sold out — a direct positive for Samsung Electronics and SK Hynix specifically, not just for sentiment generally. The brokerage framing cited in the source data captures the regime shift precisely: this has become a phase where earnings power matters more than prolonged high rates. Institutions evidently agreed, and their 305.6 billion won of net buying, concentrated where it counted, recovered the 6,900 line in the afternoon and carried the index to its close.

The KOSDAQ rally was a different animal

Here is where the divergence theme sharpens. The KOSDAQ's 4.48% surge to 894.29 was sponsored by a genuinely two-sided bid: institutions net-bought 336.9 billion won and foreigners net-bought 216.8 billion won, with only individuals selling (530.8 billion won). The buying flowed into semiconductor materials, parts and equipment names — Leeno Industrial +10.90%, Wonik IPS +9.13%, HPSP +4.87%, Jusung Engineering +4.73%.

So the same foreign cohort that was reducing KOSPI mega-cap memory exposure was simultaneously adding KOSDAQ supply-chain exposure. Read together, Thursday was less a wholesale foreign exit from the Korean semiconductor story than a repositioning within it, executed on a day when rates gave a reason to trim the biggest, most rate-sensitive positions. The KOSDAQ side of the ledger is the healthier structure: price gains backed by the flows of two investor groups rather than leaning on institutional buying against two sellers.

What would confirm the read — and what would break it

The bullish interpretation is that the KOSPI rally is the start of the earnings-over-rates regime the strategists described, with foreign flows catching up to price. The skeptical interpretation is that Thursday was a narrow, institutionally-sponsored squeeze higher in two stocks while the marginal foreign dollar kept leaking out. The flows, not the price, will settle it.

  • Confirmation: foreign flows on the KOSPI turning positive in subsequent sessions, particularly in Samsung Electronics and SK Hynix themselves, would show the afternoon reversal converted sellers into buyers. Continued foreign buying on the KOSDAQ would confirm the supply-chain leg.
  • Invalidation: persistent foreign net selling into further index strength would mark Thursday as distribution dressed up as a rally. The rate backdrop is the obvious trigger — with the 10-year already at its highest since May 2002, any further climb revives the morning's logic.
  • Known event risk: the September US ISM manufacturing PMI lands October 1 and the September non-farm payrolls report follows on October 2, the biggest variable ahead of the October 27–28 FOMC. The source data also flags the Chuseok holiday period as a source of elevated foreign flow volatility, which argues against over-reading any single day's foreign number this week.

One footnote underscores how narrow Thursday's leadership was: KB Financial fell 1.66% as the standout decliner among major large caps, with financials and other defensive sectors lagging the semiconductor complex even after the afternoon turn. A rally this concentrated, sponsored on the KOSPI by one investor group out of three, has a specific vulnerability — it needs either the foreign flows to flip or the earnings story to keep delivering. Thursday gave it the second. The next few sessions of flow data will show whether it gets the first.

This post takes one theme from the session in depth. For the index-by-index wrap of the same trading day, see Seoul Closing Bell.

Disclaimer: This post is for informational and educational purposes only. It is not investment advice, a recommendation, or an offer to buy or sell any security. Figures are drawn from same-day exchange and press data and may be provisional. Do your own research before making investment decisions.

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