Kospi, Kosdaq Both Trigger Sell Sidecars as Chip Twins Sink 7%

South Korea's two main stock indexes both triggered sell-side sidecars within 24 minutes of each other on Friday, as a fresh Houthi attack on Saudi oil tankers sent crude above $100 a barrel and hammered the country's chipmaking giants. The Kospi tumbled 5.80% to 6,685.17 and the Kosdaq fell 4.76% to 752.69, with Samsung Electronics dropping 7.59% and SK Hynix sliding 7.19% as the selloff accelerated through the session.

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What happened

The Kospi's sell-side sidecar, which halts program sell orders for five minutes to slow a rapid decline, was activated at 11:23 a.m. local time. The Kosdaq followed at 11:47 a.m. Both indexes had opened only modestly lower — Samsung and SK Hynix were down around 3% at the open — before the decline sharply deepened through the morning session as oil prices continued climbing.

The trigger was Thursday's attack in the Red Sea, where Houthi forces said they struck two Saudi oil tankers, identified as the Encelia and Layla, with missiles and drones. Brent crude jumped 7% to $100.66 a barrel and WTI gained 6.3% to $92.28, marking oil's first move back above $100 in nearly two months. The Bab el-Mandeb strait the tankers were transiting carries an estimated 12% to 15% of global maritime trade, worth more than $1 trillion a year, which is why disruption there ripples so fast into risk assets far from the Middle East.

Why it matters — market reaction so far

Friday's session stands out because it's the rare day both the Kospi and Kosdaq sidecars fired in the same morning, a sign of just how broad and fast the selling pressure was rather than isolated to one board. Trading data showed foreign investors sold a net 1.75 trillion won and institutions sold a net 1.09 trillion won, while individual investors bought a net 2.81 trillion won trying to catch the dip — buying that wasn't enough to offset the institutional and foreign outflows or halt the slide.

This is now part of a multi-week pattern rather than an isolated shock. As I covered in Houthi Attack on Saudi Tankers Sends Oil Past $100, Nasdaq Sinks 2.2%, the same tanker strikes had already rattled Wall Street a day earlier, and the same underlying oil shock produced an earlier sell sidecar and an SK Hynix ADR slide just days before. Korean markets are now absorbing the same Middle East escalation on repeat, and each fresh headline out of the Red Sea is landing on markets that are already jumpy from the prior hits.

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Who's affected

Samsung Electronics and SK Hynix bore the brunt domestically, both falling more than 7% intraday as chip stocks — which carry outsized weight in both the Kospi and Kosdaq — dragged the broader indexes down with them. Beyond semiconductors, the sidecar mechanism itself signals the decline was broad-based across program-traded stocks rather than confined to a single sector.

Globally, the read-through is energy-sensitive and risk-sensitive assets: airlines, shippers, and other oil-consuming industries face higher input costs if crude holds near $100, while energy producers benefit from the price spike. Export-heavy, chip-reliant economies like South Korea are doubly exposed — higher energy import costs on one side, and a tech sector already sensitive to swings in AI-related demand and Wall Street sentiment on the other.

What to watch next

The immediate question is whether Brent and WTI hold above the $100 and $90 marks respectively, or whether the spike fades the way earlier Middle East scares have this year. Any sign of de-escalation around the Bab el-Mandeb strait — or, conversely, further attacks on tankers or shipping lanes — will likely move Korean and US markets in tandem given how tightly linked recent sessions have been. Watch also whether individual investors' dip-buying eventually absorbs the institutional and foreign selling, or whether foreign outflows keep accelerating, which would be a more worrying signal for sustained downside.

This is not financial advice — always do your own research before making investment decisions.

Friday's dual sidecar is a reminder that markets are currently trading almost entirely on the Middle East headline cycle rather than earnings or economic data. Until there's clarity on the Red Sea shipping situation, expect volatility in oil-sensitive and chip-heavy names to stay elevated, with Samsung and SK Hynix likely to keep moving in step with crude prices rather than their own fundamentals in the near term.