Coherent, Teradyne, and Ciena Are the S&P 500’s 3 Biggest Decliners on Tuesday

Eric Bleeker

Tue, August 18, 2026 at 11:27 PM GMT+3 4 min read

Quick Read

Coherent and Ciena fell over 10% Tuesday as investors rotated out of AI hardware stocks up 276% and 390% over the past year.
The 30-year Treasury hit a 19-year high Tuesday, compressing growth valuations and dragging the semiconductor ETF down 5% while software stocks edged higher.
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Shares of three AI infrastructure heavyweights are leading the S&P 500 lower into the final hour of Tuesday's session. Coherent (NYSE:COHR) is off 11%, Ciena (NYSE:CIEN) is down 10%, and Teradyne (NASDAQ:TER) is lower by 10%. All three are the day's biggest S&P 500 decliners.

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Risk Rotation Out of AI Hardware

Today's price action is a positioning story driven by rotation. Investors are rotating out of semiconductor and AI hardware names, with tech the day's worst sector while healthcare, utilities, consumer defensive and energy trade higher. The iShares Semiconductor ETF is down roughly 5.4% while the iShares Expanded Tech-Software ETF is up about 0.7%. The 30-year Treasury hit a 19-year high today, compressing long-duration growth valuations.

Sentiment also cooled after Anthropic disclosed a $65 billion annualized revenue run rate at the end of July, below whisper numbers, and the WSJ flagged roughly $3 trillion of off-balance-sheet AI commitments across nine top tech names. Add in a soft reaction to Fabrinet's fiscal Q1 2027 guide of $1.375 billion to $1.425 billion, and optics/networking took collateral damage.

Coherent (COHR)

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COHR Price Target — 24/7 Wall St.

Coherent supplies optical transceivers and photonics into the AI datacenter buildout, and the picks-and-shovels suppliers behind that spend are exactly what we profiled in a free report on seven AI infrastructure names that aren't chipmakers, here. It has been one of the market's biggest winners, up 276% over the past year and 90% year to date. Q4 FY26 results on August 12 beat, with adjusted EPS of $1.74 versus $1.62 expected and revenue of $2.05 billion, up 33.7% year over year, as detailed in the company's 8-K filing with the SEC.

That leaves a rich setup: trailing P/E of 79x and forward P/E of 32x. Generally, when stocks rotate out of risk, it's the pricest names that take the nastiest dives. As you'll see, Coherent, Teradyne, and Ciena all fit a very similar valuation profile.

Analysts remain constructive, with an average target of $411 and 78% bullish sentiment. A stock this stretched can absolutely deliver a 10%+ session on rotation days. Coherent shares have whipsawed around the past week on a combination of earnings, supply chain chatter, and investor enthusiasm around optics.

Teradyne (TER)

TER Price Target — 24/7 Wall St.

Teradyne makes semiconductor test equipment, with roughly 70% of revenue tied to AI. The move follows an extraordinary run: up 21% in the past week, 37% in the past month, 129% year to date and 306% over one year. Q2 FY26 posted July 29 delivered revenue of $1.33 billion, up 103.9% year over year. Valuation carries the weight: trailing P/E of 57x, forward P/E of 45x. The Street's consensus target sits at $450, and 76% of analysts rate it bullish.

Once again, there's little news about Teradyne itself today, but its a company with a stretched valuation that relies on massive growth from AI in the years ahead. So, if investors are selling off the sector on fears over the size of off-balance sheet obligations, Teradyne is a first company to exit portfolios.

Ciena (CIEN)

CIEN Price Target — 24/7 Wall St.

Ciena sells optical networking gear into hyperscaler datacenter interconnect. Shares are up 15% in the past week, 90% year to date, and 390% over the past year. Q2 FY26 on June 4 beat and management raised the full-year guide, with cloud providers now 46% of revenue and up 70% year over year.

Trailing P/E is 143x, though the forward P/E drops to 52x. The consensus target of $560 implies meaningful upside from here, and 13 buy or strong-buy ratings back the setup. Once again, on rotation days, the highest-multiple names bleed first.

Keep the Long-Term Picture in Mind

While each of these stocks saw large sell-offs today, every single one is up massively year-to-date and across the past couple years. Few stocks that appreciate do so without elevated volatility. If you're a believer in the long-term buildout of AI, days like today should do little to impact your conviction.