Two Stocks Are Half of Korea's Market — and They Just Took the KOSPI Down 5.8%

Wednesday in Seoul is the cleanest illustration of concentration risk you will see this year, and the lesson has almost nothing to do with Korea.

The KOSPI opened down nearly 5%, and within six minutes the exchange hit the brakes, suspending program sell orders for five minutes. It closed down 5.8%. Two companies — Samsung Electronics and SK Hynix — did most of it. They are, between them, roughly 47% of the index by market value.

That is the whole story. When your index is really two semiconductor companies wearing a national costume, a global chip selloff is not a sector event. It is a market-wide event.

What triggered it

Three things converged.

US chipmakers fell overnight. The memory-heavy names led. The Philadelphia Semiconductor Index had already dropped over 20% during July as investors shifted from rewarding AI capital-expenditure announcements to scrutinising the returns on that spending.

Long-term government bond yields hit multi-year highs across the US, Japan and Europe. Japan's 10-year touched about 2.945% on Tuesday, roughly a three-decade high. Higher discount rates hurt expensive, long-duration equities most — and semiconductors trading on future AI demand are the definition of long-duration equity.

Oil stayed elevated after talks between Washington and Tehran stalled, keeping inflation risk — and therefore rate risk — alive.

Notably, Samsung's fundamentals were not the problem. Record second-quarter profit and multi-year memory supply contracts remain in place. This was a valuation reset, not an earnings reset.

The part that matters for your portfolio

Here is the piece almost nobody outside index circles talks about, and it directly affects millions of North American investors.

Two of the world's largest emerging-market ETFs do not hold the same countries.

• Funds tracking MSCI emerging-market indexes include South Korea. MSCI kept Korea in its Emerging Markets category at its June 2026 review, declining even to add it to the developed-market watchlist. Korea sits at roughly 20.3% of the MSCI EM index — its third-largest country weight.
• Funds tracking FTSE Russell emerging-market indexes exclude South Korea entirely, because FTSE has classified Korea as a developed market since 2009.

That means two funds, both honestly labelled "emerging markets," both tracking a reputable index, can differ by roughly a fifth of the portfolio. In practical Canadian and US terms: the iShares core MSCI EM products carry large Samsung and SK Hynix positions; the Vanguard FTSE EM products carry none.

On a day like Wednesday, that difference is not academic. It is the entire performance gap.

MSCI's reasoning, per CEO Henry Fernandez, is not about Korea's economy — he has described Korea as one of the most developed markets in the world. It is about market plumbing: the won trades only during Seoul business hours, plus investor identification requirements, restrictions on in-kind transfers, and limits on exchange data use.

What to actually do about it

Look up which index your emerging-market fund tracks. It takes two minutes on the fund page. If it says FTSE, you own no Korea. If it says MSCI, roughly a fifth of your EM sleeve is Korea, and about half of that is two chip companies.

Then check for overlap. If you also own a global semiconductor or technology fund, plus an S&P 500 fund with heavy chip exposure, you may be far more concentrated in semiconductors than you realise across accounts. Our portfolio cleanup guide walks through how to measure this properly.

Do not conclude that concentration is unique to Korea. The top ten holdings of the S&P 500 are around 40% of that index. The KOSPI is a more extreme version of a problem most index investors already own. We wrote about the US version in our piece on S&P 500 concentration risk.

What to watch

• Whether the memory chip selloff continues. Samsung had an investor tour scheduled for August 20.
• Japanese government bond yields. A three-decade high in the 10-year is a global valuation input, not a domestic curiosity.
• MSCI's next classification review. Korea has been lifting barriers, including ending a market-wide short-selling ban. An eventual upgrade would trigger substantial mechanical fund flows.

Frequently asked questions