Amazon's stock was down 1.14 percent, bringing its market capitalisation to $690.4 billion (498.34 billion pounds), while software maker Microsoft's 1.83 percent fall depressed its market capitalisation to $690.3 billion.

Bolstered by blockbuster quarterly results, Amazon's stock gained 3.8 percent over the three sessions ended Tuesday, even as Wall Street struggled through a rout that has raised fears that a nine-year bull market may be ending.

Microsoft lost about 3.1 percent over the three sessions ended Tuesday.

Amazon's market cap at points on Wednesday during intraday trade already topped that of Microsoft, but it has never closed at a higher value.

Amazon's explosive growth in retail and cloud computing has sent its shares 77 percent higher over the past year, outpacing Microsoft's 42 percent rise.

Apple Inc's $819 billion market capitalisation remains Wall Street's largest, followed by Alphabet Inc, the parent of Google, at $736 billion.

(Reporting by Noel Randewich; Editing by Leslie Adler)

By Noel Randewich

Stocks treated in this article : Microsoft Corporation, Apple, Amazon.com, Alphabet