Experts warn AI's dominance of the US stock market is creating risks all of its own.
At last month's White House AI Summit, some of the richest individuals on earth were clustered around US President Donald Trump.
Each of them had built their fortune in the tech industry.
Some of the biggest names at the table were major players well before the AI boom began, such as the leaders of Amazon, Meta and SpaceX.
Others have risen in prominence in the past few years, such as those representing AI labs like Anthropic and OpenAI.
And then there were the chipmakers, selling computing power to a frenzy of data centre operators around the world.
They are making the picks and shovels of the AI boom.
One of them is Jensen Huang. He is the CEO of Nvidia, which sells a large share of the world's top-tier AI chips. He has been described as the most powerful man in AI.
Lisa Su was the only woman among the AI executives. She is the CEO of another chipmaker, AMD.
Micron Technology CEO Sanjay Mehrotra has overseen a spectacular rise as demand for computing power took off.
Taken together, the group's estimated net worth is north of $2.5 trillion.
(Keep in mind, we're using Australian dollars throughout this story.)
Anthropic and OpenAI are private companies, so you won't find them on the stock exchange.
However, most of the listed companies in the AI space have seen their stock prices soaring in recent months.
Steve Johnson, chief investment officer of investment fund Forager, said AI companies were some of the fastest-growing businesses the world's ever seen.
"We've never seen anything like it," he said.
In the US, these AI-related companies have become so huge that they are comparable to the banks and mining companies in Australia's market, Mr Johnson said.
But their success has not been replicated across all parts of the US economy.
Some experts point to how the AI boom is masking weaknesses elsewhere, and how its outsized influence on the market may bring risks all of its own.
Let's take a look at why.
Here is a map of the S&P 500 — the top 500 listed companies in the US.
The size of each box corresponds to an individual company's market capitalisation.
That's the combined value of all its shares (or, to oversimplify a bit, how much it is worth overall).
Tech stocks dominate the market, accounting for about 44 per cent of the total value.
Six of the eight biggest US companies are in the tech industry — and that's using a narrow enough definition that it excludes Amazon and Tesla.
AI chipmaker Nvidia is the most valuable company in the world, worth about $7.5 trillion.
But size is not the only factor that matters.
Over the past six months, four companies grew more than Nvidia (in absolute terms).
In order, they were: Apple, Microsoft, Micron, and AMD.
To see just how much their stock prices have increased … let's switch to 3D.
The height of each box now shows how much each company's stock price has increased or decreased in the past six months.
That means their 3D size (or volume) represents their change in overall value.
It may not look like it, but Apple has grown the most. It grew by 30 per cent, rising by more than $1.4 trillion in just six months.
Micron and AMD have more than doubled their valuation in the past six months, leaving their boxes tall yet narrow.
Around 230 of the 500 stocks on the S&P500 have seen their stock prices go down since April.
They lost a combined $2.9 trillion in value.
However, their losses were offset by the combined gains of just Meta, Microsoft and Apple.
Add in the other three biggest winners — Micron, Nvidia and AMD — and you have already accounted for 57 per cent of the S&P 500's total gains since April.
Together, these six companies have grown by more than $5 trillion in that time.
Take these away, and the overall market would look very different.
Without them, the S&P500 would have grown just 4.35 per cent in the past six months — that is less than half the actual figure of 10 per cent.
The dominance of a single sector is not new, but the scale of market concentration was becoming unusual, RMIT economics professor Angel Zhong said.
"At the peak of the dot-com bubble in 2000, the top 10 stocks made up about 27 per cent of the S&P 500. Recently, it is about 39 per cent," she said.
Unlike during the dot-com bubble — when crazy valuations were based largely on hype — some AI companies are already highly profitable. Chipmakers Nvidia, Micron and AMD all fall into that category.
But this is not true across the board.
"Revenue at the leading AI labs is still a fraction of what is being spent on their behalf," Professor Zhong said.
And these AI labs — like OpenAI and Anthropic — are among the biggest customers of the chip-makers and the data centre operators.
The other major buyers are the tech giants going all-in on AI, like Microsoft, Meta and Alphabet (that's Google), and their staggering levels of investment are outpacing their world-beating profits.
"This boom started out being paid for mostly from profits," Professor Zhong said. "Now it increasingly relies on outside money, including a lot of debt."
Circular financing
Another concern is where this outside money is coming from.
Nvidia has been called the 'bank of AI', since it is investing hundreds of billions of dollars in its biggest customers.
This means massive sums of money are essentially going around in circles.
Here's one such example:
- Nvidia partnered with OpenAI, announcing that it would invest up to $144 billion in the AI lab's infrastructure.
- OpenAI then signed a $430 billion contract to use Oracle data centres.
- Finally, Oracle spends $58 billion on buying Nvidia chips to place in those data centres.
This is just one example of many, Professor Zhong said.
"[These] companies are each other's investors, suppliers and customers at the same time.
"It's harder to tell how much AI demand is genuine and how much is funded by the sellers themselves."
This ties the companies' fortunes together. "If one key player, especially OpenAI, ran into trouble, the effects would ripple through the whole network," Professor Zhong said.
And, as we have seen, this network of AI-related companies now represents a major part of the entire S&P500. And that could expand even further if OpenAI and Anthropic proceed with their plans to go public and list on the stock market.
Everyday investors exposed
Nvidia's Huang told Bloomberg that wobbles in AI stocks over the past week will pass because the technology is "going to impact in a very positive way every single industry and every single country".
While Forager's Steve Johnson is quick to point out the risks of this concentrated AI-heavy market, he agrees the technology has the potential to change the world.
"There's no doubt about AI's impact on the broader economy. It is going to be a part of our everyday lives."
But that does not necessarily translate into returns for those who invest in it.
"The question is whether these are going to be great businesses or not … I think the technology can be transformational, and people [can] still not do well from the investments."
It all comes down to whether these companies — the AI labs, the chip-makers, the data centre operators and the tech giants — can collectively turn a promising new technology into a money maker that matches the massive sums being invested.
"I think from an investor perspective, the hype around this is almost certain to end in disappointment," Mr Johnson said.
"It's going to be very fascinating to see how it unfolds."
About the data
- Tech stocks in the S&P500 were identified using FTSE International's Industry Classification Benchmark (ICB).
- Stock market data was extracted from LSEG Refinitiv, covering the time period from April 16, 2026 to October 15, 2026.
- Individuals' net worth is drawn from the Bloomberg Billionaires Index (as of October 12, 2026) and Forbes Real Time Billionaires List (as of October 14, 2026).
Credits
- Reporting: Julian Fell and Zena Chamas
- Design and production: Teresa Tan
- Production: Jessica Riga
- Chart development: Julian Fell
- Editing: Matt Liddy
- Photo: Getty Images/Kevin Dietsch