As US stock prices keep relentlessly rising, I feel the next stock market crash getting closer. In May, the S&P 500 hit 11 fresh peaks. In 2026, the index has set 23 new record highs, breaching 7,600 points on 2 June.

As share prices soar, buying into listed companies becomes a risky business. And given the irrational exuberance among investors, I suspect that the coming market meltdown is inevitable. What might trigger the next collapse?

Price sensitive

Academics have long debated what bursts bubbles and causes financial crashes. Could it be sudden reversals of equity inflows into outflows? Excessive use of leverage and gearing? Economic downturns, changes in interest rates, or external shocks?

I’m not an academic and don’t own a crystal ball, so I’m unable to predict the future. Also, one of my heroes, Nobel Prize-winning physicist Niels Bohr, allegedly warned, “Prediction is very difficult, especially if it’s about the future”.

Then again, after nearly 40 years of investing, I have directly experienced six major market meltdowns. For me, the underlying cause was always the same: share prices became excessively high, reaching crazy levels and detaching from reality. When financial gravity was finally restored, prices came crashing down to earth.

Three Titans

Right now, I suspect the event most likely to trigger the next stock market crash is the imminent arrival of three new US-listed companies.

Three huge private groups — Elon Musk’s SpaceX, Sam Altman’s OpenAI, and Dario Amodei’s Anthropic — are set to float a small proportion of their shares in the US this summer. Current valuation estimates for these ‘three Titans’ are colossal: around $1.8trn, $1trn, and $1trn, respectively.

One enormous problem is that this trio of AI Goliaths doesn’t make much profit, as their revenues are tiny compared to their prospective market values. In other words, a huge batch of shares in largely unprofitable businesses is about to be dumped on passive investors and active buyers.

When this last happened on a grand scale (in 1999, as the dotcom bubble peaked), it triggered one of the worst market downturns in history. From its peak in March 2000 to the trough three years later, the US stock market lost almost half its value. I do hope this doesn’t happen again.

A crash-resistant share?

When the crash finally arrives, I suspect that go-go growth stocks and financial shares might be hit hardest. In my search for crash-resistant UK shares, I came across one long-term market survivor: biopharma giant GSK (LSE: GSK).

GSK is built on four growth pillars: respiratory, immunology and inflammation; oncology; HIV; and infectious diseases. As I write, the shares stand at 1,894p, valuing this FTSE 100 stalwart at £76.8bn. This stock is up 26.8% over one year and 38.5% over five years, but is 17% below its 52-week high of 2,282p.