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S&P Dow Jones Indices announced on June 5 that Marvell Technology and Flex Ltd. will be added to the S&P 500 index, effective prior to market open on June 22, 2026. Marvell shares climbed roughly 6% in after-hours trading on the news.
The additions are part of the S&P 500’s quarterly rebalance. Marvell (MRVL) will replace Pool Corp. (POOL), while Flex (FLEX) takes the spot vacated by The Campbell’s Company (CPB).
Every index fund and ETF benchmarked to the S&P 500 is now obligated to buy shares of both companies, creating a wave of forced demand that often pushes prices higher independent of fundamentals.
Why these two, and why now
Marvell Technology is a semiconductor firm that has carved out a significant niche in AI infrastructure. The company designs custom chips and networking components that power the data centers at the heart of the current AI buildout.
Flex Ltd. provides electronics manufacturing services, acting as the factory floor for companies that design but don’t build their own hardware, assembling everything from medical devices to automotive components.
S&P 500 membership is determined primarily by market capitalization, liquidity, and sector representation, among other criteria.
The index fund effect
When a stock gets added to the S&P 500, fund managers don’t have a choice about whether to buy it. This forced buying typically happens in the days leading up to the effective date, as portfolio managers front-run the official inclusion to minimize tracking error.
The quarterly rebalance also affects other indices in the S&P family. The S&P MidCap 400 will see its own roster changes, including the addition of Roku.
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