UBS Urges Rebalancing as S&P 500 Tech Concentration Hits 40% Dotcom Peak

On June 18 2026, UBS warned that the top ten US tech stocks now comprise nearly 40% of S&P 500 market value, matching late-1990s bubble extremes driven by AI enthusiasm. The bank remains constructive on global equities medium-term yet downgraded European IT to Neutral after 40% year-to-date gains and stretched valuations. Investors are advised to trim megacap holdings in names such as Nvidia and Microsoft and broaden exposure into AI infrastructure, industrials, automation and power supply chains. Taiwan Semiconductor’s 30% May sales rise and Nvidia’s crossing of the $5 trillion market-cap threshold underscore continued AI capex support, but UBS flags historical reversal risks from such concentration.