Micron , SanDisk , Seagate , and Western Digital have emerged as the four hottest investments in the artificial intelligence revolution. Although these companies often trade together, they are not the same. All four companies are among this year’s S&P 500’s 10 best performers, driven by soaring demand for memory and storage needed to support building AI data centers. SanDisk is leading the pack, soaring about 575% since the beginning of the year. Micron rose 240%, followed by Seagate, which rose about 210%, and Western Digital, which rose more than 170%. If you zoom out, the benefits are even more impressive. Since the beginning of 2025, Micron is up about 920%, Western Digital is up 820%, and Seagate is up nearly 740%, compared to the S&P 500’s 25% gain. SanDisk, which began independent trading in February 2025, has soared more than 4,300%. The group began operating at scale as hyperscalers accelerated spending on AI data centers and demand for memory and storage skyrocketed. Supply could not keep up, creating shortages and giving producers significant pricing power, helping to boost profits and inventories. The momentum strengthened into 2026, but has reversed sharply in recent weeks, with the four stocks now trading around 20% to 40% below their late June peaks. These are all benefiting from the same AI spending boom, but occupy different parts of the memory and storage ecosystem. The easiest way to differentiate companies is by taking advantage of the speed-cost trade-offs in three key technologies: DRAM (dynamic random access memory), NAND flash memory (a type of non-volatile storage), and hard disk drives. One end is DRAM. That’s Micron’s bread and butter. It is the fastest and most expensive of the three. NAND (SanDisk’s sole focus and also part of Micron’s business) is slightly slower but cheaper. Hard disk drives (HDDs) from Seagate and Western Digital are slower to access, but are the cheapest way to store large amounts of data. Importantly, these technologies are not necessarily substitutes for each other. DA Davidson analyst Gil Luria told CNBC that modern computers and data centers “need all of that.” “They’re doing something different,” echoed Sanjay Mehrotra, CEO of Micron, who said AI is creating demand across the memory and storage ecosystem. “AI is driving the entire hierarchy of memory requirements, from high-bandwidth memory to DRAM to solid-state drives (SSDs), and this is an exciting time for memory and the critical needs of all AI systems,” Mehrotra said Thursday on “Squawk on the Street,” appearing with Jim Cramer from the site of the company’s planned $10 billion research facility in his hometown of Boise, Idaho. MU YTD Mountain Micron’s year-to-date stock performance. Micron sells both DRAM and NAND, but the DRAM business is becoming more important as demand for AI accelerates. Micron is the only company of the four we own in the club’s portfolio. DRAM is essentially a computer’s short-term working memory. Holds data that the processor needs to access quickly while performing calculations. DRAM is also a type of chip that is stacked together to create high-bandwidth memory (HBM). HBM acts like an ultra-wide data highway designed to move vast amounts of data between graphics processing units (GPUs) and central processing units (CPUs) at high speeds. This makes HBM fundamentally important for training and running increasingly sophisticated AI models. “The CPU is more important to the data center than the CPU,” Luria said. Mehrotra, an engineer by trade who has worked in the chip industry for more than 40 years and previously co-founded SanDisk, said AI has fundamentally changed the memory business. “Today, there is no AI without memory. AI systems need more memory. They need higher performance memory. They need lower power memory,” Mehrotra later told Jim on “Mad Money.” “So the value of memory, the equation has completely changed.” Luria made a similar point, arguing that memory has become part of the computing engine itself. “It’s no longer just a storage area,” he says. “It’s actually how the model works. It’s now the essence of the model. It’s not just a periphery. It’s not an accessory.” This is an important distinction for Micron because memory has historically been considered a commodity. Micron and the world’s three largest DRAM manufacturers, South Korea’s SK Hynix and Samsung Electronics, competed primarily on price, contributing to the violent boom-bust cycles that have long characterized the industry. Now, rather than customers simply soliciting bids and purchasing from the supplier offering the lowest price, HBMs are increasingly required to be designed in parallel with the processors and systems on which they run. This creates deeper relationships between memory suppliers and customers and increases visibility into future demand. Mehrotra said Micron still cannot produce enough to meet demand. “All of our end-market customers will buy everything we make,” the CEO said, adding that data center customers currently want about 50% more supply than Micron can commit to. Micron seeks to further reduce the cyclicality of its business through long-term strategic customer agreements (SCAs). The company announced 16 such deals with its June earnings report. Mehrotra told “Mad Money” that the company has since signed additional contracts. SNDK YTD Mountain SanDisk’s year-to-date stock performance. Stepping down the speed and cost spectrum is NAND. SanDisk is essentially a pure NAND flash memory user after splitting from Western Digital in February 2025. Although NAND is slower than DRAM, it has the important advantage of retaining information even when the power is turned off. In AI data centers, NAND is useful for storing large datasets used to train models and other information that needs to be stored later. Simply put, DRAM holds the data that the processor currently needs, while NAND stores large amounts of data that may be needed later. SanDisk and Japan’s Kioxia have been co-manufacturing NAND through a long-standing partnership. Samsung, SK Hynix and Micron are also major suppliers. STX WDC YTD Mountain Seagate and Western Digital’s year-to-date stock performance. Seagate and Western Digital are on the opposite end of the spectrum. Both companies primarily make hard disk drives and are more direct competitors than Micron and SanDisk. HDDs cannot access data as quickly as DRAM or NAND. However, they are significantly cheaper, making them an economical way for data centers to store vast amounts of information that does not need instant access. Unlike NAND, which uses silicon-based semiconductor chips with no moving parts, HDDs are not semiconductors. Instead, data is stored magnetically on rotating disks. Western Digital’s sole focus on hard drives is relatively new. The company previously owned SanDisk and was into both HDD and NAND before completing the separation of its flash business in 2025. Conclusion AI enhancements can benefit all four companies as their products serve different purposes. “When you build a data center, you buy a certain level of HBM, DRAM, NAND, and disk drives,” said DA Davidson’s Luria, speaking from the position of chief technology officer. “We buy a mix of all of them, depending on what the data center is trying to accomplish.” The opportunity extends beyond the data center. Mehrotra said he expects self-driving cars, robots and AI-enabled consumer devices to require increasingly large amounts of memory in the coming years. Still, Luria sees Micron as particularly well-positioned due to its exposure to HBM, which is increasingly important for AI computing and no longer operates like the commodity memory of the past. When asked if that gives Micron a competitive advantage, his answer was simple. “It’s huge.” Luria also believes that investors have yet to fully “grasp” the changes and growing importance of memory in AI infrastructure. That’s the main reason we acquired Micron on August 11th. The company’s stock still trades at a significant discount to many of its semiconductor peers, reflecting skepticism about the durability of its memory cycles. However, if HBM and Micron’s long-term customer contracts make earnings more sustainable, we believe there is room for investors to push the stock’s price multiple even higher. (Jim Cramer’s Charitable Trust is a long MU. See here for a complete list of stocks.) 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