Japanese and South Korean equities fell sharply on Monday, driven by markedly different forces: a stronger yen weighed on Tokyo's export-heavy market following confirmed currency intervention, while renewed doubts over artificial intelligence valuations dragged down Seoul's chip-dominated benchmark.

Japan: Intervention-Fueled Yen Surge Pressures Exporters

Japan's Nikkei 225 briefly shed more than 1,600 points, falling as much as 2.58% intraday on Monday, after confirmation that Japanese and US authorities had conducted coordinated yen-buying intervention on Friday, US Eastern time. The dollar weakened sharply against the yen as a result, moving from around 160.20 yen late Friday afternoon in Tokyo to briefly below 156 yen by mid-morning Monday — its lowest level in roughly three months. The Nikkei has now fallen approximately 12.9% from its 2026 peak.

The intervention marked the first confirmed coordinated action by Tokyo and Washington since the yen's protracted slide began earlier in the decade, a depreciation driven largely by the wide interest-rate gap between the Bank of Japan's ultra-loose monetary policy and the Federal Reserve's higher rates. The 160-yen-per-dollar threshold has been widely watched by currency markets as a level that increases the likelihood of official action, having last prompted intervention rounds in 2024.

An official at a Japanese securities house said export-oriented stocks, particularly automakers, were sold on concerns that the stronger currency would erode profitability on overseas sales once converted back into yen. A stronger yen carries mixed implications across corporate Japan: large importers benefit from cheaper costs to bring goods into the country, while exporters such as Toyota and Honda typically see their products become more expensive and less competitive abroad, weighing on their share prices. That dynamic is likely to persist as long as the yen holds its gains, keeping exporter-heavy indices under pressure even as importers stand to benefit from reduced input costs.

South Korea: AI Valuation Concerns Trigger Sharp Chip Selloff

In Seoul, the KOSPI fell more than 4% on Monday, extending losses after its worst monthly performance since the 2008 global financial crisis. The renewed selling targeted the market's two dominant semiconductor names, which together account for more than half of the KOSPI's total weighting, leaving the broader index highly exposed to swings in sentiment around AI-related demand.

Samsung Electronics dropped about 8% and SK Hynix lost more than 7%, erasing much of the relief rally the two stocks had staged on Friday following their latest earnings reports. Samsung and SK Hynix are the world's two largest memory chipmakers, controlling the bulk of global DRAM and NAND supply alongside US-based Micron, meaning that swings in their valuations reverberate across the global semiconductor supply chain. The selloff came despite strong underlying results from both companies. Samsung reported a more than 250-fold jump in semiconductor operating profit and announced multi-year supply agreements with major data-centre operators, while warning that global memory shortages could persist through 2028. SK Hynix also posted record quarterly earnings.

Even so, investors appeared unconvinced that the strength in results was sufficient to offset broader concerns that expectations for AI-driven chip demand had run ahead of what the sector can sustainably deliver. Those concerns mirror a global reassessment of AI infrastructure spending that has also weighed on US-listed chipmakers and hyperscaler equities in recent weeks. The renewed selling follows the index's 22% plunge in July alone — a decline driven by concerns over AI valuations, slowing hyperscaler spending, and heavy retail investor positioning that together produced one of the sharpest corrections the market has seen in decades.

The scale of July's KOSPI drawdown suggests sentiment around AI-linked semiconductor names remains fragile and prone to sharp reversals even on strong fundamental news, a pattern traders will be watching closely heading into the rest of the week.