Shares of semiconductor company SanDisk Corporation (SNDK) are having quite the Monday evening. The stock is trading sharply higher in after-hours trading following an announcement that the company is getting the ultimate Wall Street promotion: admission to the S&P 500.

The Index Shuffle

S&P Global announced Monday that SanDisk will replace The Interpublic Group of Companies (IPG) in the S&P 500. The move happens on November 28, and it's one of those corporate musical chairs situations where everyone shifts around. SanDisk is currently hanging out in the S&P SmallCap 600, and when it moves up, PTC Therapeutics Inc (PTCT) will take its spot in that index.

Interpublic Group is exiting the S&P 500 because it's being acquired by Omnicom Group Inc (OMC), with the deal expected to close soon. When you get bought out, you lose your seat at the big kids' table.

Here's why this matters for SanDisk: massive funds and ETFs that track the S&P 500—like the SPDR S&P 500 ETF Trust (SPY)—will need to buy shares of the company to maintain their index weighting. That's a lot of forced buying, and the market knows it. Companies that get added to major indexes almost always see their stock pop on the news, and SanDisk is no exception.

Already on a Tear

This comes at a time when SanDisk is already riding high. The company reported fourth-quarter results on November 6 that beat analyst expectations on both revenue and earnings per share. That's becoming a pattern—SanDisk has beaten revenue estimates in eight of the past ten quarters and earnings estimates in eight of the last ten quarters as well.

Morgan Stanley is clearly a believer. The firm maintained its Overweight rating on Monday and bumped its price target from $263 to $273.

The stock jumped over 13% during regular Monday trading, then tacked on another 9% in after-hours action to reach $247.25. That's still within the stock's 52-week range of $27.90 to $284.76, but it's a meaningful move nonetheless.

And if you're wondering about the bigger picture: SanDisk shares are up over 530% year-to-date in 2025. Yes, you read that correctly. It's been that kind of year for the semiconductor company.