Amazon stock topped $800 for the first time Thursday, surging to $805 in mid-afternoon trading.
The rise brought Amazon's (AMZN) market cap to $381.6 billion, according to Yahoo Finance. That makes it the world's fourth most valuable company, behind Apple at $616.87 billion, Alphabet at $541.9 billion and Microsoft at $450.56 billion.
The bump may have been linked to a new buy rating for Amazon on Wall Street, the Seattle company's seventh this year, according to StreetInsider.com
Argus Research upgraded Amazon to buy Thursday.
"While the growth engine at Amazon is unmatched, the stock has been difficult to time from a valuation perspective. Based on our historical comparables analysis and discounted free cash flow valuation, we believe Amazon's growth prospects are accelerating more rapidly than the share price, thus creating a favorable entry point, Argus analyst Jim Kelleher wrote.
Amazon shares are up 17% year-to-date, compared to a 6% gain for the S&P 500.