The S&P 500 (^GSPC -2.71%) index just posted its strongest September in 15 years, gaining 3.5% during the month. Technology stocks led the way, with some absolutely crushing the index with over 50% gains. Here's a look at the three top-performing S&P 500 stocks from September and what drove them higher.

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1. Warner Bros. Discovery
Shares of Warner Bros. Discovery (WBD -3.23%) surged 67.8% in September on takeover speculation. On Sept. 11, The Wall Street Journal reported that Paramount Skydance, which was acquired by the Ellison family (owners of Oracle), was preparing a "majority cash bid" for Warner Bros.
Warner Bros. stock hit a 52-week high of $20.24 on Sept. 25. While it's unclear whether a merger will ever happen, management has plans to split into two companies by mid-2026, separating its streaming business and studios from its global TV networks business.
2. AppLovin
AppLovin (APP -5.09%) joined the S&P 500 index on Sept. 22, but the stock went higher right after S&P Dow Jones announced the upcoming addition on Sept. 5. With several analysts also lifting their price targets on AppLovin, the stock skyrocketed 50.1% in September.
The company's platform helps mobile app developers and marketers monetize their apps, mainly through advertising. But the stock is under pressure this month after a Bloomberg report stated that the Securities and Exchange Commission is probing AppLovin's data collection practices.
3. Western Digital
Shares of Western Digital (WDC -3.64%) soared 49.4% in September and hit a 52-week high of $137.40 on Oct. 2. At least seven analysts raised their price targets on the stock last month amid booming demand for artificial intelligence and cloud computing, both of which require large-scale data storage. Western Digital is among the largest manufacturers of hard-disc drives (HDD), flash products, and storage devices in the world.
Analysts at Morgan Stanley raised Western Digital's price target from $99 to $171 per share, citing the stock's low valuation despite the huge potential demand for HDDs amid rising cloud spending.