Investors can thank strong earnings, interest-rate cuts and marketwide optimism for an unseasonably strong September and a S&P 500 mere points from record highs.
But before investors stroll into the historically strong fourth quarter, it’s worth taking account of the stocks that made the index’s banner performance possible.
You might thank the megacaps, which are dominating the market narrative: players like Nvidia (NVDA) , Alphabet (GOOGL) and Meta (META) . Credit to these firms: They’re among the largest holdings in the index for a reason, but there’s more than what’s happening at the top.
In fact, many of the middling holdings in America’s most-watched indexes put up sharply higher showings in Q3. Here are some of the best-performers from thethree months:
Western Digital
AI investments aren’t benefiting only chipmakers like Nvidia (NVDA) , cloud giants like Oracle (ORCL) , and hyperscalers like CoreWeave (CRWV) . By many accounts, the biggest beneficiaries this year have been storage companies like Western Digital (WDC) .
The company, which makes hard disks for storage, has become the S&P 500’s second-best-performing stock this year, rising 87.6% in Q3 and bringing its year-to-date return to 168.46%.
Much of that growth has been driven by data-center buildouts, which are seeing hyperscalers — the largest providers of cloud infrastructure and services — purchase larger hard disks. WDC’s fiscal 2025 revenue grew 51% to $9.52 billion. And revenue growth is expected to remain impressive, with the company forecasting the coming quarter’s revenue to grow 22%.
Warner Bros. Discovery
HBO and CBS parent Warner Bros Discovery (WBD) also boasted a big Q3, rising 70.42%.
Most of the entertainment giant’s gains have come on the back of a planned breakup of its legacy and streaming media platforms. It’s a move that has long been speculated about and would enable the company to provide separate focuses on legacy media and streaming.
However, it’s also worth touching on the $380 billion elephant in the room: The rumor mill is spinning with murmurs that competitor Paramount Skydance (PSKY) might make a bid for the company. Such a bid would be backed by Larry Ellison, one of the world’s richest men, a topic we tackled in recent weeks.
Related: Paramount Skydance is working on a media ‘megadeal’ with boost from world’s richest man
Seagate Technology
It turns out that there’s plenty of room at the top for another storage company and AI beneficiary. Seagate Technology (STX) rose 63.6% in the third quarter, thanks to many of the circumstances that buoyed Western Digital.
However, Seagate is doing its competition one better. The company has become a quiet favorite, eclipsing retail favorites like Palantir (PLTR) and Micron Technology (MU) to become the best-performing stock in the S&P 500, up 173% year-to-date.
Related: This stock just displaced Palantir to become the S&P 500’s top-performing stock
Corning
This is the company famous for making the glass on your Apple iPhone, but it offers more than Gorilla Glass. Materials-sciences company Corning (GLW) jumped 56% in the third quarter, buoyed by double-digit EPS and net-sales growth.
Core sales grew 12% year-over-year, while core EPS grew 28% over the third quarter, led by the Optical Communications business. (Go figure: It’s an AI beneficiary, too.)
Its Hemlock and Emerging Growth Businesses (net sales +31% YoY) and Specialty Materials (+9%) were also standouts for GLW in its latest quarter.
Teradyne
Recently featured in a Bloomberg article on AI trades, Teradyne (TER) has attracted a fervent investor crowd. The producer of tools to test chips in manufacturing plants jumped 53% in the quarter. That helped put the stock back in the green, +9.3% year-to-date.
Honorable Mentions
Outside the top five stocks, dozens of stocks outstripped the index’s quarterly showing.
Among them were chipmaker Intel (INTC) , which is in the midst of a rebound. It was joined by Paramount Skydance (PSKY) , mentioned above.
And Invesco (IVZ) , Newmont Mining (NEM) and Arista Networks (ANET) weren’t far behind.
Index newcomers like AppLovin (APP) and Robinhood (HOOD) have also continued to rally in light of their recent addition to the index on Sept. 22.
But with just seven trading days under their belt, they’re better-suited candidates for next quarter’s roundup. But they were up 50.14% and 37.63% respectively over the past month, and they’re definitely ones to watch.