Wall Street's main indexes closed lower on Tuesday, August 18, with semiconductor stocks leading a broad technology decline as fading hopes for a US-Iran peace deal pushed both oil prices and Treasury bond yields to multiyear peaks, reviving concerns about borrowing costs and inflation.

How the Major Indexes Closed

The S&P 500 lost 53.09 points, or 0.69%, to close at 7,691.97, while the Nasdaq Composite shed 355.20 points, or 1.33%, to finish at 26,289.71 — marking the biggest daily percentage decline for both indexes since July 29. The Dow Jones Industrial Average held up relatively better, falling 116.38 points, or 0.22%, to 53,343.40. The moves pushed Wall Street's main indexes to their lowest levels in two weeks.

The Domino Effect Behind the Selloff

The trigger traced back to stalled diplomacy around the Middle East conflict. "It starts off almost like a domino effect. Talks break down. That leads to oil prices going up. That leads to higher inflation expectations and bond yields rise," explained Burns McKinney, portfolio manager at NFJ Investment Group. He added that "every time bond yields rise, that tends to disproportionately hit the technology names," given how sensitive growth-stock valuations are to the cost of capital.

Bond Yields Hit Historic Levels

Fading hopes for Middle East peace pushed oil prices higher, which in turn drove US 30-year Treasury bond yields to their highest levels since 2007. The 10-year Treasury yield touched its highest level since January 2025. Rising borrowing costs directly reduce how much investors are willing to pay today for expected future growth in technology company profits — a dynamic that hit high-multiple AI and chip names especially hard.

Semiconductors Bear the Brunt

The Philadelphia SE Semiconductor Index (SOX) tumbled 5.4% and was on pace to erase more than $680 billion in market value if losses held, as investors fled stocks that had rallied sharply on booming AI-related demand in recent weeks. Chip giant Nvidia fell 2.3%, while memory chipmaker Micron Technology dropped nearly 7% after having risen almost 18% over the previous five sessions — a sharp reversal for one of the sector's recent standout performers. Data storage firms Sandisk and Western Digital were also among the hardest-hit names, both falling more than 7%.

Sector Breakdown

Among the S&P 500's 11 major sectors, information technology created by far the biggest index-point drag and was the benchmark's worst-performing sector, falling 1.9%. In sharp contrast, the energy sector gained 1.8%, benefiting directly from the same rising oil prices that were dragging down tech — a clear illustration of how the Middle East standoff is creating winners and losers within the same trading session. Volatility also ticked up, with the VIX rising 4.28% to 15.84.

Oil and the Dollar

WTI crude rose 0.54% to $84.51 a barrel, while Brent crude edged up to $91.36. The US Dollar Index gained 1.42%, reflecting continued safe-haven demand amid the geopolitical uncertainty. Gold, meanwhile, fell 0.80% to $4,385.45 an ounce, a notable pullback after its recent rebound, as rising Treasury yields made non-yielding assets like gold comparatively less attractive.

The Bigger Picture

Tuesday's selloff underscores just how tightly Wall Street's fortunes remain tied to developments in the Strait of Hormuz standoff. With stalled US-Iran talks now feeding directly into oil prices, bond yields, and technology valuations in a single trading session, analysts say markets are likely to remain highly reactive to any fresh headlines out of the region — for better or worse — in the sessions ahead. For live market data, see CNBC Markets.

With semiconductor stocks having erased hundreds of billions in value in a single session, Tuesday's decline serves as a pointed reminder of just how concentrated — and vulnerable — this year's AI-driven market rally has become to shifts in the macro and geopolitical backdrop.