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Why Tech Stocks Crashed Friday

Aaron Pressman
Altaba, the Company Formerly Known as Yahoo, Will Start Trading Today

Top performing technology stocks plummeted on Friday afternoon after a leading investment bank warned that share prices of companies like Apple, Amazon, and Facebook had risen too quickly.

At the close of trading, shares of Apple were down 4%, lopping more than $30 billion from the market capitalization of the world’s most valuable company. Shares of Google parent Alphabet were down 3%, as were shares of Facebook and Amazon. Microsoft slipped 2%. The tech-heavy Nasdaq index, which is dominated by the five stocks, was down almost 2%.

Investors have been growing increasingly uneasy about the skyrocketing value of the largest tech companies, but Friday’s sell-off appears to have been sparked by a report from Goldman Sachs chief investment officer Robert Bouroujerdi warning of the growing risks on those five leading tech stocks. Almost 40% of the gain in the entire Standard & Poor’s 500 Index this year is attributable to the five tech stocks, even though they make up only 13% of the index’s market value, he wrote.

“Five companies poised to dominate disruption – Facebook, Amazon, Apple, Microsoft and Alphabet – have added a total of $600 billion of market cap this year or the equivalent GDP of Hong Kong and South Africa combined,” Bouroujerdi noted. “Parallels to the ‘Nifty-fifty’ and 1999-2000 are growing as their performance is even more pronounced on a risk-adjusted basis.”

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Other had been warning about the prominence of the big five for the past few weeks, comparing the situation to prior bubbles like the rise of Internet stocks in the late 1990s. At the end of May, Miller Tabak’s analyst Matt Maley raised the comparison and wrote: “I just wonder how many people have said to themselves, ‘If AMZN gets to $1,000, I’m going to take at least some profits.'”

Amazon first reached the $1,000 level in mid-day trading in late May and closed for the first time over $1,000 on June 2.

Friday’s sell-off came after months of strong returns in the tech sector. While the S&P 500 was up just 9% so far this year, Apple aapl was up 34% this year as of June 7, Bouroujerdi noted. Google googl was up 26%, Amazon amzn 35%, Facebook fb 33%, and Microsoft msft 16%.

But the afternoon sell-off hit many more stocks than just the big five. Among semiconductor companies, Nvidia nvda lost 6%, Intel intc as down 2% and AMD amd dropped 5%. Netflix nflx lost 5%, Salesforce.com crm was off 4% and Tesla tsla fell 3%.