Microsoft was the first publicly traded company to reach a $500 billion market capitalization.
Microsoft crossed the $500 billion valuation level in 1999 during the late-1990s technology boom. Its Windows operating system and Office productivity software had become dominant products in personal computing, producing enormous revenue and strong investor expectations before the dot-com bubble burst.
The achievement belongs to Microsoft’s public-market valuation, not to a private-company estimate or an enterprise-value calculation. Microsoft had gone public in 1986, and its share price rose dramatically during the 1990s as personal computers spread through homes and businesses.
The late-1990s market environment also explains why records from that period can be difficult to compare with modern ones. Technology shares were priced amid unusually optimistic expectations, and many valuations later fell sharply. Microsoft remained profitable and central to enterprise computing, eventually building major businesses in cloud computing, gaming, and professional software.