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Apple became the first U.S. company to reach a market capitalization of $2 trillion on Aug. 19.
Micorost and Amazon are nearing the $2 trillion club with market caps of more than $1.7 trillion each; Google reached $1 trillion in January and Facebook is worth nearly $900 billion.
The five companies make up more than 20 percent of the S&P 500, according to stock market newspaper Investor's Business Daily.
Apple and Amazon have seen significant growth over the past decade and the past year.
Apple's market cap has surged 69 percent -- about $695 billion -- in 2020 alone. Amazon shares are also up about 60 percent in 2020, and the company's market cap has grown by more than $600 billion this year.
Tech stocks have spiked amid the coronavirus pandemic at a pace that some investors have compared to the internet explosion, or "doctom bubble" of 1999.