South Korea's National Assembly Discusses Unrealized Gains Tax, KOSPI Plunges 10% in Single Day Triggering Circuit Breaker
Claire Weston
On June 23 a multi-party tax-reform forum in Seoul proposed taxing unrealized gains on stocks and real estate. The KOSPI crashed 10% to 8,203.84 — its worst day since March 4 — triggering a circuit breaker, with Samsung Electronics down over 7% and SK Hynix off more than 10%.
What exactly does this tax proposal want to tax?
The core idea: adopt "comprehensive income taxation" — if your net asset value rises, that counts as income and is taxable, whether you sell or not.
This means → paper gains on stocks or property could, in theory, trigger a tax bill even if you never sell a single share or unit.
The logic, per senior researcher Lee Sang-min of Korea's National Finance Research Institute: taxing only at the point of sale creates a "lock-in effect" — holders refuse to sell, and capital stays frozen instead of flowing to more productive uses.
In plain terms = the current rule is "sell, then pay tax." The proposal wants to change it to "if it went up, you earned it."
How would it actually be implemented?
The forum laid out a gradual path: unrealized gains would be recognized as income, but taxpayers could defer payment until the asset is actually sold — or pay later with interest.
For assets that are hard to value at market prices (unlisted shares, certain real estate), the current "tax on sale" rule could remain, or a pilot targeting high-net-worth holders could come first.
Park Ki-san, head of the Korean Confederation of Trade Unions, went further, calling to reinstate the financial-investment income tax and add higher rate brackets for ultra-high earners.
Why did the market react so violently?
The KOSPI fell 10% on the day, closing at 8,203.84 — its largest single-day drop since March 4 — and triggered the circuit breaker.
Samsung Electronics dropped over 7%; SK Hynix lost more than 10%. Both heavyweights leading the sell-off signals a systemic retreat from tech.
This reflects something bigger than the tax discussion alone: the market is repricing the lofty valuations built up during the AI boom. Once the cost of holding assets may rise, the most expensive names get sold first.
Were there warning signs before the crash?
Hana Securities strategist Lee Jae Mahn in Seoul flagged a key overheating signal: SK Hynix's valuation had already exceeded Samsung Electronics'.
His view: for the KOSPI to keep rising, Samsung must lead SK Hynix in share-price gains — and the market expects Samsung to overtake SK Hynix in Q2 earnings.
In plain terms = when the number-two player trades richer than number one, sentiment has usually run ahead of fundamentals.
What else is piling on — regulators and external pressure?
Before the crash, Financial Supervisory Service Governor Lee Chan-jin said the regulator was coordinating with the Financial Services Commission and the Korea Exchange to assess stability measures, including tighter trade-pattern monitoring — specifically to contain contagion risk from leveraged ETFs tracking Samsung and SK Hynix. He said the side effects were "intensifying."
Externally, Bank of America chief U.S. economist Aditya Bhave forecast the Fed will hike 25 bp each in September, October, and December — 75 bp more — and hold rates through all of 2027.
Goldman Sachs, Morgan Stanley, and Deutsche Bank have all warned recently that services inflation, wage growth, and energy-price swings may slow the inflation decline. A stronger dollar puts systematic pressure on Korean tech valuations.
What is the next key test?
Pepperstone strategist Dilin Wu pointed to Micron's earnings this week as the next critical checkpoint — a strong Micron report would directly validate Samsung's and SK Hynix's fundamentals.
This means → Micron's numbers answer a core question: does the AI hardware investment boom still have room to grow, or has it peaked?
Whether Korean stocks stabilize depends on two threads resolving together: whether the tax discussion becomes real legislation, and whether the Fed's rate path further compresses tech valuations.
Content is for reference only, not financial advice.