For much of 2026, the Nikkei 225 looked unstoppable. AI investment lifted Japanese semiconductor names, a weak yen supported exporters, and the index climbed well past the record set during Japan's 1980s asset bubble.
That momentum is now fading.
Japan's benchmark closed at 64,011.34 on September 11, down 1.93%. It had traded above 68,700 in mid-August, leaving the index nearly 7% below that level in less than a month.
The pullback doesn't mean Japan's equity story has collapsed. But it does reveal how dependent the Nikkei 225 has become on a small group of expensive tech stocks — at a moment when oil prices and interest-rate expectations are moving against them.
The Nikkei 225 Is More Concentrated Than It Looks
The index contains 225 companies, but its daily direction is often determined by fewer than ten.
Unlike the S&P 500 or TOPIX, the Nikkei 225 is weighted by share price rather than market capitalization. A company with an expensive share price can have a larger influence than a company with a higher total market value.
Official index data from September 8 placed Advantest at a 12.50% weight. Fast Retailing accounted for 8.47%, Tokyo Electron for 8.32%, and SoftBank Group for 8.08%. Those four companies represented more than 37% of the index.
Technology stocks as a group carried a weight of 56.59%.
That concentration explains why the Nikkei can move sharply even when the broader Japanese market is relatively stable. On September 11, the Nikkei lost 1.93%, while TOPIX fell only 0.65%. The difference came largely from weakness in high-priced semiconductor and AI-related shares.
The Nikkei is still a useful measure of Japanese market sentiment. It is not an evenly distributed picture of corporate Japan.
The AI Trade Is Now Working in Both Directions
Japanese chip stocks benefited heavily from the global expansion in AI infrastructure. Advantest supplies semiconductor testing equipment. Tokyo Electron produces chipmaking equipment. Kioxia provides memory products, while companies such as Fujikura and Ibiden have gained exposure to data-center and advanced-packaging demand.
These businesses gave global investors a way to trade AI growth through the Japanese market.
The same concentration now creates downside risk. When US chip stocks fall or investors question the pace of AI spending, the reaction quickly reaches Tokyo. On September 11, technology and AI-related shares led the decline. Kioxia fell nearly 7%, while several semiconductor-material and equipment companies recorded even larger losses.
The underlying demand for AI hardware has not disappeared. The market is questioning how much future growth is already included in share prices.
That distinction matters. A strong industry can still produce weak stock returns when expectations run ahead of earnings..
Advantest’s Weight Has Become an Index Issue
Advantest’s rise has made it the largest component of the Nikkei 225. Its influence is now large enough that Nikkei Inc. plans to apply a weight cap from October 1.
The change is intended to stop one stock from becoming too dominant. A similar rule has previously been applied to Fast Retailing.
For passive funds tracking the Nikkei 225, the adjustment may require portfolio rebalancing. Advantest’s underlying business does not change because of an index rule, but its mechanical demand from index-linked products could change.
The decision also confirms that the Nikkei’s concentration is no longer a minor technical detail. A move in one semiconductor-equipment company can materially affect Japan’s headline stock index.
Investors evaluating Japanese equities should therefore compare the Nikkei with TOPIX. If both indices rise together, participation is probably broadening. If the Nikkei moves far more sharply, a few high-priced stocks may be doing most of the work.
The Bank of Japan Is No Longer a Passive Support
The Bank of Japan meets on September 17 and 18. Its policy rate currently stands around 1.0%, following five increases since March 2024.
For years, Japanese equities operated under extremely low interest rates. Cheap financing supported valuations, weakened the yen and encouraged investors to seek returns in stocks.
That environment is changing.
In a September 10 speech, Bank of Japan Policy Board member Kazuyuki Masu said Japan had moved fully out of deflation. He described underlying inflation as close to the central bank’s 2% target and argued that policy rates should rise further over time.
His comments do not guarantee an increase at the September meeting. They show that the debate has moved beyond whether Japan should normalize policy. The question is now how quickly that normalization should proceed.
Higher rates can help banks by improving lending margins. They can also pressure highly valued growth stocks, leveraged businesses and sectors that benefited most from cheap capital. A stronger yen would add another challenge for exporters by reducing the yen value of overseas earnings.
Oil Is Complicating the BOJ Decision
Japan imports most of its energy, leaving its economy sensitive to crude oil and liquefied natural gas prices.
Masu noted that slightly more than 70% of Japan’s crude imports have historically passed through the Strait of Hormuz. Disruption in the region has pushed energy costs higher and raised concerns about inflation, transportation expenses and corporate margins.
Higher oil prices create an uncomfortable mix for the Japanese market. They increase costs for manufacturers and households while giving the Bank of Japan another reason to monitor inflation closely.
A weak yen can support exporters, but it also makes imported energy more expensive. If oil and the dollar rise at the same time, Japanese companies may face higher input costs even as their overseas revenue benefits from currency translation.
This is why the current Nikkei pullback cannot be explained by semiconductor stocks alone. Energy and monetary policy are now part of the same trade.
The Headline Index Carries the Higher Valuation
Official figures for September 11 put the Nikkei 225’s market-cap-weighted price-to-earnings ratio at 16.97. The index-weighted P/E was higher at 21.27, while the index-weighted price-to-book ratio stood at 2.64.
The difference is revealing. Companies with the greatest influence on the Nikkei are valued more richly than the broader basket when measured by market capitalization.
That premium may be justified if semiconductor earnings continue to grow quickly. It becomes harder to defend if AI investment slows, margins weaken or global interest rates remain high.
The Nikkei’s index-based dividend yield was only 1.48%. Investors are therefore relying more heavily on earnings growth and capital appreciation than on income.
The current valuation is not comparable with the extremes of Japan’s late-1980s bubble. It still leaves less room for disappointment than a broad index number might suggest.
A High Index Does Not Mean a Broad Market
The Nikkei 225 remains one of the world’s strongest-performing major indices over the longer term. Japanese corporate reform, improved shareholder returns and global demand for semiconductor equipment still provide genuine support.
Its recent pullback exposes the price of concentration.
More than one-third of the index rests with four companies. Technology represents over half its weight. Oil is increasing Japan’s imported inflation, and the Bank of Japan is openly discussing further policy normalization.
The next move will depend on more than whether the Nikkei returns to its August high. Traders should watch whether TOPIX confirms the direction, whether semiconductor earnings support current valuations and how the yen responds to the September BOJ meeting.
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Frequently Asked Questions
Why is the Nikkei 225 falling?
The latest pullback has been driven by weakness in semiconductor and AI-related shares, rising global bond yields, higher oil prices and uncertainty ahead of the Bank of Japan meeting.
What was the latest confirmed Nikkei 225 closing level?
The Nikkei 225 closed at 64,011.34 on September 11, 2026, down 1.93% for the session. Market levels can change quickly after publication.
Is the Nikkei 225 market-cap weighted?
No. It is a price-weighted index. Companies with higher share prices can exert greater influence even when other companies have larger market capitalizations.
