U.S. AI stocks drive market gains as concentration risks build

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Highlights

Technology stocks now represent 44 percent of U.S. market value, with six tech giants—led by Nvidia at $7.5 trillion—driving most recent gains.
Since April, nearly 230 S&P 500 companies lost $2.9 trillion in value, offset by Meta, Microsoft, Apple, Micron, Nvidia, and AMD accounting for 57 percent of index gains.
Nvidia's planned $144 billion investment in OpenAI links a tightly coupled AI funding chain with Oracle's $430 billion contract and $58 billion Nvidia chip purchase, increasing systemic risk if any major AI player falters.

Market gains narrow around AI leaders

As reported by ABC News, technology stocks account for about 44 per cent of the total U.S. market value, and six of the eight biggest U.S. companies are in the tech sector. Nvidia, now valued at about $7.5 trillion in the source text, stands as the world's most valuable company, while Apple, Microsoft, Micron and AMD are also among the biggest contributors to recent market gains.

Over the past six months, around 230 of the 500 companies in the S&P 500 have seen their share prices fall since April, wiping a combined $2.9 trillion from their value. Those declines are offset by gains from a handful of companies, with Meta, Microsoft and Apple alone covering the losses, and Micron, Nvidia and AMD helping lift the six biggest winners to 57 per cent of the index's total gains since April.

Without those six companies, the S&P 500 would have risen only 4.35 per cent over the past six months, less than half of the reported 10 per cent increase. Investors cited in the source say sector dominance is not new, but the current level of concentration is becoming unusual for the U.S. market.

Funding structure raises wider risks

Unlike the dot-com era, several AI-linked companies are already highly profitable, particularly chipmakers such as Nvidia, Micron and AMD. But Professor Zhong says that revenue at leading AI labs remains far below the spending committed on their behalf, while major buyers including Microsoft, Meta and Alphabet continue to invest at a pace that exceeds even their strong profits.

That funding model is increasingly relying on outside capital and debt, rather than being financed mainly from profits. The source describes Nvidia as a so-called bank of AI because it is investing hundreds of billions of dollars in key customers, creating a tightly connected financial chain across AI labs, data centre operators and chip suppliers.

One example in the source links Nvidia's planned investment of up to $144 billion in OpenAI infrastructure, OpenAI's $430 billion contract for Oracle data centres, and Oracle's $58 billion spending on Nvidia chips. Analysts warn that if one major player, especially OpenAI, runs into trouble, the effects could spread through the network and weigh on a much larger portion of the S&P 500, particularly if private AI groups such as OpenAI and Anthropic later pursue stock market listings.

Nvidia Chief Executive Jensen Huang tells Bloomberg that recent volatility in AI shares will pass because the technology is set to affect every industry and every country positively. Forager Chief Investment Officer Steve Johnson also says AI is likely to become part of everyday life, but he warns that technological transformation does not automatically guarantee strong investor returns.

Our earlier article on the U.S. AI data-center boom highlighted that the buildout is facing mounting headwinds from expensive financing, construction delays, and power-grid constraints. We noted that analysts viewed only a fraction of planned projects as realistic and that setbacks at infrastructure firms were already exposing refinancing and cost-overrun risks—raising doubts about how quickly computing capacity can scale without eroding investor confidence.

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