SanDisk Soars 858% to the Top. S&P 500's Top 10 Gainers for the First Half of 2026 Revealed, Why Wall Street Warns of a Deep Correction in the Second Half.

TradingKey - The US stock market in the first half of 2026 was like a roller coaster ride. After a gloomy first quarter, the second quarter staged its strongest rebound in nearly six years. Among them, SanDisk ( SNDK) topped the S&P 500 gainers list with an astonishing 858% surge. Among the top ten gainers in the S&P 500, chip stocks occupied more than half of the seats, while the optical communications sector also emerged as a dark horse, with three stocks making it into the top ten.

However, as the market enters the second half, even the most optimistic investors on Wall Street are beginning to be on alert: a substantive correction may be looming ahead-of-time correction may be looming.

US Stocks Record Best Second Quarter in Six Years

In the first quarter of this year, U.S. stock investors were plagued by multiple negative factors. The outbreak of the war in Iran shocked global risk appetite, while the rapid iteration of artificial intelligence technology triggered market concerns over the disruption of business models in the software and professional services industries, causing the S&P 500 Index to temporarily plunge into a phase of panic selling.

However, entering the second quarter, market sentiment reversed completely, with capital flooding into the artificial intelligence supply chain, particularly the memory chip sector, which benefited from a supply-demand gap.

As of the close on June 30, the S&P 500 Index accumulated a gain of 14.87% in the second quarter, marking its best quarterly performance since 2020; the Nasdaq Composite Index surged 21.41%, also setting a new record for nearly six years; the Dow Jones Industrial Average rose 12.9%, its largest gain in 14 quarters.

For the first half of the year as a whole, the Dow accumulated a gain of 8.85%, the S&P 500 rose 9.55%, and the Nasdaq advanced 12.79%.

The semiconductor sector became the absolute protagonist of this market rally. The Philadelphia Semiconductor Index skyrocketed 88% in the second quarter, marking its best single-quarter performance in history, with an accumulated gain of 101% in the first half of the year, on track to deliver its strongest annual performance since the dot-com bubble in 1999.

Chip Stocks Dominate the S&P 500's Top Ten Best-Performing Stocks

Among the S&P 500 components, SanDisk emerged as the top-performing stock in the first half of the year with an astounding gain of 858%. This memory chip company, which was spun off from Western Digital just last year, saw its stock price skyrocket driven by explosive demand for solid-state drives (SSDs) in AI data centers.

Jefferies analyst Blayne Curtis pointed out that SanDisk's market share in the enterprise SSD market has risen from 4% last quarter to 8% and is expected to recover to its historical level of 10%-15%, thus raising its price target to $3,000.

SanDisk's TLC (triple-level cell) storage technology is gaining increasing market favor, and high hopes are also pinned on its upcoming Stargate series of QLC (quad-level cell) enterprise SSDs.

Following closely behind is Micron Technology ( MU ), which surged more than 300% in the first half of the year. As a global memory chip giant, Micron benefited from robust demand for High Bandwidth Memory (HBM) driven by AI servers, with its HBM capacity for the entire fiscal year 2026 already fully booked.

Despite the substantial rise in its stock price, Micron's forward P/E ratio stands at just 8.1 times, well below the S&P 500's 20.3 times and the information technology sector's 22.8 times, reflecting investors' concerns over the traditional cyclical nature of its business.

However, the new customer agreements recently announced by Micron CEO Sanjay Mehrotra are expected to significantly enhance the sustainability and predictability of the company's financial performance.

Intel ( INTC) ranked third with a 278% gain. As the company's 18A-P process node enters the risk production phase, Intel's technological strength in advanced processes has been initially validated, bolstering market confidence in its foundry transformation prospects.

In addition, Intel's strategic collaborations with companies such as Foxconn and Siemens have laid the foundation for its presence in the AI infrastructure space.

Among the top ten gainers in the S&P 500, chip stocks occupied more than half of the seats. In addition to SanDisk, Micron, and Intel, chip giants such as Western Digital ( WDC ), AMD ( AMD ), and others also delivered stellar performances.

Source: LSEG

How Far Can a Rare "Reverse Revision" Support US Stocks?

Wall Street strategists generally believe that stronger-than-expected corporate earnings growth is the core driver of the second-quarter market rally. FactSet analyst John Butters noted that while analysts typically lower earnings forecasts for the current quarter as the quarter-end approaches, a rare upward revision occurred in the second quarter of this year, with earnings expectations continuously raised.

Market expectations for the S&P 500's second-quarter earnings growth rate currently stand as high as 23.1%. If realized, this will mark the second consecutive quarter of earnings growth exceeding 20%.

Ben Snider, senior US equity strategist at Goldman Sachs, pointed out in a report that over the past 12 months, upward revisions to earnings expectations accounted for the entirety of the S&P 500's returns. Measured by the forward P/E ratio, the index has actually become cheaper over the past year, which means earnings must continue to beat Wall Street's already elevated expectations to support current valuations.

Notably, investor focus is shifting from hyperscale cloud computing companies to the broader AI ecosystem. The market has begun to assess companies' actual willingness to spend on AI products, how that spending is distributed across the ecosystem, and whether these expenditures can generate reasonable returns for service providers.

Will Quarter-End Rebalancing and Rampant Leverage Trigger a US Stock Market Correction?

Despite the overall strength of the market, there are growing signs that risks are accumulating.

Mark Hackett, chief market strategist at Nationwide, noted that while tailwinds still outnumber headwinds, some technical risks warrant vigilance.

First is the pressure of quarter-end rebalancing. Paisley Nardini, managing director of multi-asset solutions at Simplify Asset Management, pointed out that with equities significantly outperforming bonds this quarter, large asset owners such as sovereign wealth funds and pensions will be forced to sell stocks and buy bonds to correct asset allocation drift.

The iShares 20+ Year Treasury Bond ETF, which primarily invests in 30-year U.S. Treasuries, gained less than 1% this quarter, standing in sharp contrast to the stock market's performance and highlighting the rebalancing pressure.

Second is the uncertainty surrounding the Federal Reserve's policy path. Signals from the newly appointed Fed Chair, Kevin Warsh, during his first press conference unsettled the market; his preference for a more low-profile, restrained communication style has left some investors worried about the direction of policy.

The futures market swiftly priced in higher rate hike expectations for 2026, and Wall Street remains deeply divided, with some institutions expecting no rate hikes this year, while economists at Bank of America project three rate hikes.

Meanwhile, options trading volume has climbed sharply, investor margin debt continues to rise, and the assets under management (AUM) of leveraged ETFs have expanded rapidly alongside the surge in semiconductor stocks. For instance, the AUM of the Direxion Daily Semiconductor Bull 3X Shares more than doubled over the past year, soaring from $14.1 billion to nearly $34 billion.

Charlie McElligott, an analyst at Nomura Securities, warned that leveraged products could amplify U.S. stock volatility, noting that the Nasdaq's single-day plunge of over 4% on June 5 was a preview of this vulnerability.

In addition, while earnings growth has supported rising stock prices, the valuations of some equities have reached historic highs. Micron Technology's forward P/E ratio stands at 8.1x, well below the S&P 500's 20.3x and the information technology sector's 22.8x, reflecting investor concerns over the traditional cyclical nature of its business. On the other hand, although stocks like SanDisk have surged, their P/E ratios have actually declined due to faster-growing earnings expectations.

What is the outlook for US stocks in the second half of the year?

Faced with accumulating risks, Wall Street strategists generally believe that the stock market's upward path over the coming year may not be linear.

David Laut, Chief Investment Officer at Kerux Financial, warned that the market volatility since June is "just the tip of the iceberg." He added that a larger correction of 10% to 20% would not be surprising, given that it has been over a year since the last double-digit pullback.

While raising her S&P 500 target price this week, RBC strategist Lori Calvasina also cautioned investors to prepare themselves for a 5% to 10% pullback over the next year.

However, some institutions remain optimistic. Mark Hackett stated that corporate earnings have supported this rapid re-rating of stock prices, and he maintains an overall bullish stance. Goldman Sachs believes that as AI technology continues to penetrate, corporate investment in the AI sector will keep increasing, and companies within the related supply chain are poised to benefit.

Overall, the performance of U.S. stocks in the first half of the year demonstrated the strong resilience of the tech sector and the massive opportunities brought by AI technology, while also exposing market vulnerabilities and potential risks. While participating in the tech rally, investors also need to remain vigilant against potential pullbacks, ensuring proper risk management and asset allocation.