Microsoft became the first US business to reach a US$500 billion market capitalization in 1999.
Microsoft crossed the US$500 billion mark during the late-1990s technology boom, when investors placed exceptionally high values on software companies and internet-related growth. The company was then led by co-founder Bill Gates and was dominant in personal-computer operating systems and productivity software.
Its core products included MS-DOS, Windows, and Microsoft Office. Those products created a powerful platform business in which software was licensed across millions of computers, producing substantial recurring demand and high profit margins.
The dot-com crash later reduced valuations across the technology sector, showing why market capitalization is not a permanent measure of corporate size. Microsoft’s later expansion into Azure, subscriptions, gaming, and enterprise services helped it regain a leading position among the world’s most valuable companies.