Shares of Amazon.com Inc. AMZN, +4.61% ran up 1.2% to a record close of $1,052.80 on Wednesday, to propel the e-commerce giant's market capitalization above $500 billion for the first time. That makes Amazon just the fourth company currently above that threshold, behind Apple Inc. AAPL, +0.82% at $800.12 billion, Google's Alphabet Inc. GOOGL, +1.38% at $667.67 billion and Microsoft Corp. MSFT, +1.88% at $571.70 billion. Warren Buffett's Berkshire Hathaway Inc. BRK.B, +0.08% is a distant fifth at about $428 billion. With 477.98 million shares outstanding as of April 18, according to Amazon's latest quarterly filing, Amazon's market cap is now $503.21 billion. Amazon's achievement comes a day before it reports second-quarter results. The stock has soared 15.8% over the past three months, to add $68.59 billion to Amazon's market cap, while the Nasdaq Composite COMP, +1.26% has rallied 6.6% and the S&P 500 SPX, +0.80% has gained 3.8%.