日経平均、米AI関連の下落に反応し1915円安 半導体株が売り集中

On July 16, the Nikkei 225 fell 1,915 yen to close at 66,835, erasing all gains from the previous day and marking a sharp reversal after three days of advances. The decline unfolded in two phases: an initial 800-yen-plus drop at the open that pushed the index below the 68,000 mark, followed by listless afternoon trading as selling pressure eased but buy-backs remained limited. The Tokyo Stock Exchange Prime saw 446 gainers against 1,070 decliners, with trading volume at approximately 9.56 trillion yen.

The trigger was a cascade of weakness in U.S. semiconductor and AI-related shares. SanDisk and Micron fell in U.S. trading, immediately dampening sentiment in Tokyo despite broader U.S. market strength. Japanese semiconductor heavyweights bore the brunt: Kioxia HD slumped 15% to rank as the Prime's largest loser, while Lasertec, Advantest, and Tokyo Electron all fell sharply. AI-adjacent suppliers including Ibiden, SUMCO, and Murata Manufacturing also declined significantly. The article notes that even TSMC's solid earnings report elicited only a muted reaction, suggesting that sector-wide selling pressure overwhelmed company-specific positive news.

Not all sectors capitulated. Software and SaaS shares reversed the prior day's underperformance, with NEC, Nomura Research Institute, Free, and Moneyforward posting substantial gains. Corning's sharp drop in the U.S. market triggered a secondary selloff in Japanese cable and wire makers—Furukawa Electric, Fujikura, and Sumitomo Electric all fell sharply—demonstrating how peripheral supply-chain names can amplify moves when U.S. catalyst stocks collapse. Among other movers, TENTIAL surged on strong third-quarter earnings, and newly listed ChatPlus opened at 2.1 times its public offering price before closing at the daily limit up.

The market's underlying structure reveals a high-stakes dependency on AI-related momentum. The prior day (July 15) had seen the Nikkei rise 1,008 yen to 68,751 after softer U.S. consumer-price data eased inflation concerns and lifted Nvidia and other AI names; that enthusiasm spread to Tokyo and drove broad AI buying. The reversal one day later—triggered by the same sector deteriorating in the U.S.—erases the two-day gain in a single session. Market participants observe that with a three-day holiday approaching, some selling likely reflected attempts to reduce overnight risk. The immediate focal point is whether the index can hold above 66,268 yen, the recent low set on July 14; a breach could trigger further cascading selling.

The Tokyo market's sharp reversal on July 16 marks a striking departure from the momentum of the previous day, when the Nikkei rose 1,008 yen to 68,751 driven by AI-related strength following softer-than-expected U.S. inflation data. The structure of the decline reveals a market now heavily dependent on a single thematic driver: as soon as semiconductor and AI stocks faltered in the U.S. market, Japanese investors followed suit almost mechanically. The article identifies this as a key vulnerability—when the index's core movers (semiconductor leaders and AI-adjacent companies) weaken together, individual stocks struggle to rebound even on strong earnings, as evidenced by TSMC's solid results failing to arrest the decline.

A secondary observation underscores the market's attempt to find alternative pockets of strength. While the headline captures the semiconductor rout, the body shows that software and SaaS shares—NEC, Nomura Research Institute, Free, and Moneyforward—attracted sustained buying. This rotation suggests investors are not simply fleeing equities but repositioning within them. The three-day round trip (up 1,008 yen, then down 1,915 yen) also hints at pre-holiday caution: with a long weekend approaching, some selling may reflect risk-off behavior rather than a conviction shift. The market's next test is whether the recent low of 66,268 yen (set July 14) holds; if it does not, the slide may accelerate.

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