As the year draws to a close, it is time to take a step back on a particularly turbulent U.S. market. The year 2025 was notably marked by Donald Trump's return to the presidency of the United States. His geopolitical and macroeconomic decisions have had a major impact on the trajectory of Wall Street, as well as on global markets.

Adding to this political backdrop was growing investor concern about the future of the technology sector and the risk of a speculative bubble around artificial intelligence plays. This nervousness was symbolized at the very start of the year by a first major shock: the arrival in the West of the conversational agent DeepSeek, presented as an open-source, lower-cost alternative capable of reshuffling the deck for the industry.

Despite these fears and bouts of turbulence, the S&P 500 and the Nasdaq 100 showed resilience. In 2025, the two indexes rose by roughly 18% and 22%, respectively. Solid performances, albeit slightly below 2024, when they jumped 25% and 27%.

Technology remains, unsurprisingly, the best-performing sector within the S&P 500 this year. It is followed by basic materials, buoyed in particular by mining companies that benefited from the rise in the price of gold as well as strong demand for rare earths and copper. Next come more defensive sectors, such as utilities and financial services, reflecting particularly pronounced volatility in 2025.

While technology remains the market's main engine, doubts around artificial intelligence have left their mark. They are visible in the performance of certain mega-caps. Apple (+9%) and Meta (+13%) significantly underperformed a technology sector up about 35%. The reason lies largely in their relative delay in the strategic pivot to AI.

Conversely, some players fully capitalized on the new wave of investment. Micron (+239%), Seagate (+232%) and Western Digital (+204%) rank among the index's biggest gainers, propelled by massive demand for memory chips, now indispensable to building AI infrastructure.

The year 2026 now looks set to be a pivotal stage for the sector. With many questions already swirling, artificial intelligence will have to demonstrate its ability to generate tangible profits, or at least move closer to doing so. A necessary step to justify elevated valuations and sustain investor confidence.