Amazon shares closed in a bear market Monday as the e-commerce giant added to a 20 percent decline from all-time highs reached back in September.

At Monday's close of $1,636.85 per share, the stock had fallen 20.1 percent from an intraday high of $2,050 per share hit on Sept. 4, 2018. Amazon, which topped $1 trillion in market capitalization on Sept. 4, is now worth $809 billion.

Amazon's stock fell 4.4 percent on Monday, down more than 18 percent since the start of the fourth quarter, but slightly off its lows of the day. Almost 73 percent of the technology sector is in correction levels (10 percent off a security's 52-week high) or worse.

As the stock market resumes its sell-off, investors are taking profits on some of the most successful trades of the bull market, including Amazon and the other FANG members.

Twenty-six of the 66 technology stocks in the S&P 500 are in bear market territory, including Advanced Micro Devices, Micron, Nvidia, Qualcomm, Symantec, Broadcom. The Technology Select Sector SPDR ETF, which tracks the performance of a variety of technology-related stocks, dropped 3 percent Monday.

Apple, the largest public company in the U.S., is 16 percent off its own Oct. 3 intraday high; Intel is off 19 percent from its own 52-week high.

— CNBC's Gina Francolla contributed reporting.

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