Which technology-heavy U.S. stock index lost about 78 percent during the dot-com crash?

The Nasdaq Composite lost about 78 percent during the dot-com crash.

The technology-heavy Nasdaq Composite peaked at 5,048.62 on March 10, 2000. It fell to 1,114.11 on October 9, 2002, a decline of approximately 78 percent. The index contained many internet, software, telecommunications, and other technology companies whose valuations had risen dramatically.

The dot-com bubble had been fueled by enthusiasm for internet businesses, abundant venture capital, and expectations of rapid growth. Many companies had little revenue or no profits, yet their shares traded at extremely high valuations. When confidence weakened, investors sold technology stocks and financing became harder to obtain.

The Nasdaq’s decline was larger than the roughly 49 percent fall in the S&P 500 from its 2000 peak to its 2002 low. The crash did not mean that every internet company failed; firms with durable business models eventually became important parts of the technology sector.