Two Chips Have Carried the S&P 500's 2026 Rally. Why History Says It May Not Be Over

Nvidia and Micron have kept the rally alive

The S&P 500 is still being pulled higher by a narrow band of semiconductor stocks. Chipmakers now make up 18% of the S&P 500, and a handful of semis have accounted for more than half of the index's 8% gain this year. That concentration is the core tension: it can carry the market to new highs, but it also leaves the broader tape exposed if demand expectations shift.

Just as important, the rally still has momentum. S&P 500 futures were 0.4% higher, and a hold-through-the-close would put the benchmark on track for a record close for a second consecutive day. That repetition matters psychologically. When the same leadership group keeps winning, investors often treat continuation as safer than it truly is.

Why concentration has not ended the bull run

The reason this setup can still work is that the concentration is not purely speculative. It is tied to real AI spending and demand. As long as that spending narrative holds, heavy leadership can keep lifting the index even before participation broadens meaningfully.

That does not make the market risk-free. An 18% weighting in chip stocks leaves the benchmark vulnerable to sharp reversals in a sector known for cyclicality. But vulnerability is not the same as an immediate top. For now, momentum and earnings support are still pointing higher, even if the path remains uneven.