https://www.gamespot.com/articles/valve-boss-gabe-newells-worth-has-reportedly-incre/1100-6454231/

Unlike Activision, EA, Take-Two, Ubisoft, Nintendo, Sony, and Microsoft, Valve is not a publicly traded company. That's part of the reason why we don't officially know Valve's net worth. Some publicly traded companies also disclose their executives' salaries, but Valve doesn't do this since it's private. In other Valve-related news, Steam users can currently try Warhammer 40,000: Dawn of War III and Warhammer: End Times - Vermintide for free.