Microsoft was the first company to reach a US$500 billion market capitalization.
Microsoft crossed the US$500 billion level in 1999 during the technology-stock boom. At the time, investors placed exceptionally high valuations on major software and internet businesses, and Microsoft was the dominant supplier of operating systems and office productivity software for personal computers.
Microsoft was founded in 1975 by Bill Gates and Paul Allen. Its agreement to provide an operating system for IBM-compatible personal computers helped establish MS-DOS, while Windows later became the company’s best-known consumer platform. Office, server software, and enterprise tools broadened its business.
The milestone belongs to the late-1990s market environment and should not be confused with Microsoft’s later trillion-dollar milestones. Market capitalization is a moving calculation based on share price and shares outstanding, so historical records may identify a trading-day crossing rather than a particular closing value.