Skyrocketing stock valuations, wild swings in the worth of trillion-dollar companies, and sudden sharp market drops have sparked growing worry that portions of the U.S. stock market may be caught in a speculative bubble.
For some time, investors have been uneasy about the massive gains seen in artificial intelligence and semiconductor stocks, questioning whether Wall Street is building up another dangerous bubble like those seen in the past.
Those worries intensified last week when technology stocks took a steep dive, driven by concerns about debt-financed AI spending and fears that the Federal Reserve may keep interest rates elevated.
Markets have since stabilized, with investors pointing to positive sentiment, broader participation across sectors, and strong corporate earnings as reasons the rally could hold — but the unease has not gone away.
Warning Indicators on the Rise
“Looking through the lens of valuations, positioning, and sentiment … all measures of asymmetry and risk are flashing amber,” said Oliver Shale, investment specialist for the U.S. at Britain-based Ruffer.
Several valuation measures have climbed close to record highs, while certain gauges of investor mood are running hot.
“None of this is to say that the end is nigh, but that is a fragile setup for any market,” Shale added.
A proprietary risk tool from BofA Global Research — which scores assets on a scale from 0 to 1, with 1 representing extreme bubble-like behavior — currently sits at 0.91 for the PHLX Semiconductor Sector and 0.82 for the Technology Select Sector.
Valuation Concerns Mount
The overall value of the U.S. stock market has climbed to levels that have historically preceded major downturns, according to the so-called Buffett Indicator — a measure named after investor Warren Buffett.
That indicator, which compares the total value of U.S. stocks to the country’s gross domestic product, stood at 218% in the first quarter — just below the all-time record of 219% set the quarter before.
The S&P 500’s price-to-sales ratio is currently at 3.22, according to Tajinder Dhillon, head of earnings research at LSEG. That figure is well above the long-term historical average of 1.84, indicating that stocks are priced at a premium.
“Nearly every S&P 500 valuation metric is higher than it’s ever been except, possibly, PE ratios,” said Mark Spiegel, managing member and portfolio manager at Stanphyl Capital Partners.
While the S&P 500’s price-to-earnings ratio — the most commonly used measure of stock value — has not hit the extreme levels seen during past bubbles, some investors remain doubtful. Solid earnings growth has helped keep that number in check, but skeptics aren’t convinced.
“There’s a solid argument that the ‘E’ (earnings) in those ratios is an unsustainable bubble in itself,” Spiegel said.
The S&P 500’s price-to-earnings ratio currently stands at 20.2 times projected earnings over the next 12 months, compared with 25.2 during the height of the dotcom bubble, according to LSEG Datastream.
The explosion in demand for AI-related chips has created enormous profits for chipmakers, but questions linger about whether the companies spending billions to buy that technology will ever see a worthwhile return.
“The folks selling the picks and shovels are in incredibly good stead. Those buying them still have to prove that the billions and billions of dollars they’re spending is worth it,” said JJ Kinahan, head of retail expansion and alternative investment products at Cboe Global Markets.
Sentiment Signals Are Mixed
Measures of investor mood and market positioning are sending conflicting signals.
A June global fund manager survey from BofA showed investors are still leaning bullish, though the level of optimism dipped slightly compared to May.
The latest American Association of Individual Investors Sentiment Survey showed a notable drop in bearish views alongside a jump in bullish sentiment. The resulting bull-bear spread reached 8.8% — above its historical average of 6.5% for only the second time in 20 weeks. However, that figure remains well below the 44.2% peak, suggesting markets are not yet in a state of euphoria.
Some investors also find encouragement in a recent widening of market leadership. After the gap between the S&P 500 and its equal-weight version surged to around 14 percentage points in early 2026, it has since narrowed to roughly 3 points — a sign that more stocks across the market are participating in the rally, not just a handful of tech giants.
“A red flag is when sentiment and positioning is at extremes, and that’s not what we see now,” said Angelo Kourkafas, senior global investment strategist at Edward Jones.
While the market may not be sending full alarm signals just yet, Brian Jacobsen, chief economic strategist at Annex Wealth Management, urged investors to keep their portfolios diversified.
“It does look like too many people are assuming fat margins and high growth rates are here to stay, while I’m a bit more skeptical about that outlook,” Jacobsen said.
