* Futures down: Dow 0.5%, S&P 500 0.8%, Nasdaq 1.6%

* Netflix ( NFLX ) falls as earnings forecast disappoints Wall Street

* Intuitive Surgical ( ISRG ) falls despite Q2 results beat

(Updates prices; adds analyst comments)

By Ragini Mathur and Avinash P

July 17 (Reuters) - U.S. stock index futures fell on Friday

as a selloff in chip stocks deepened, forcing investors to

reassess the sustainability of this year's AI-fueled rally,

while a weak forecast from Netflix ( NFLX ) added to the pressure.

After a blistering run that lifted Wall Street's main

indexes to record highs, investors have started to retreat from

crowded semiconductor trades as worries over the scale of

AI-related spending resurfaced.

Chip stocks were broadly weaker, extending the previous

session's losses, with Nvidia ( NVDA ) and Intel ( INTC ) down

2.7% and 2.8% in premarket trading, respectively. The iShares

Semiconductor ETF declined 2.4%.

The Philadelphia SE Semiconductor index hit a nearly

two-month low on Thursday and was set for its worst week since

March 2025. The gauge has shed more than 19% from its late June

record.

Strong results from TSMC, the world's top advanced

AI chipmaker, and ASML, the leading supplier of

high-end chipmaking equipment, did little to ease concerns over

the durability of the chip-stock rally.

"This is morphing from just a chip sell-off into something

far broader. That is particularly obvious in indices like the

Nasdaq, which has come so far, so fast in such a short space of

time," said Chris Beauchamp, chief market analyst at IG.

Netflix ( NFLX ) also weighed on sentiment after the

streaming giant forecast third-quarter revenue and earnings

below Wall Street expectations. Its shares were down nearly 10%.

The renewed bout of volatility drove the CBOE Volatility

Index, Wall Street's fear gauge, to more than a

week-high, rising 1.36 points to 18.09.

At 7:07 a.m. ET, Dow E-minis were down 272 points,

or 0.52%, and S&P 500 E-minis were down 59.5 points, or

0.79%. Nasdaq 100 E-minis were down 454.25 points, or

1.55%.

Thursday's chip stocks-led losses had already set a weaker

tone. The main indexes were on track for weekly declines,

despite an initially upbeat start to the second-quarter earnings

season from major banks and benign inflation data earlier in the

week.

Geopolitical risks also loomed large. Iran said it had

launched fresh attacks on U.S. facilities in the Gulf after a

sixth straight night of U.S. strikes on Iranian military

targets.

The escalation followed the breakdown of a brittle ceasefire

reached last month and renewed concerns over energy flows

through the Strait of Hormuz, fanning price pressures.

"Undoubtedly, there'll be concerns that we are poised to see

a much broader sell-off that will be amplified by what's going

on with the U.S. and Iran," Beauchamp added.

Meanwhile, U.S. President Donald Trump's fresh accusations

that China meddled in U.S. elections risked complicating a

fragile truce with Chinese leader Xi Jinping, just two months

before a planned summit in Washington.

Among other premarket movers, Intuitive Surgical ( ISRG )

fell 11.2%, even after the medical device maker topped Wall

Street estimates for second-quarter profit and revenue on strong

demand for its surgical systems.

(Reporting by Ragini Mathur and Avinash P in Bengaluru; Editing

by Joyjeet Das)