The fine was issued by the tournament referee Monday, a day after Williams was cited by the chair umpire Eva Asderaki for a code violation for verbal abuse during the game.
Williams, who lost 6-2, 6-3 to Sam Stosur, earned a total of $1.4 million at the U.S. Open: $900,000 for reaching the final plus a $500,000 bonus for finishing first in the standings of the U.S. Open Series.
In a statement, Grand Slam Committee Director Bill Babcock determined Williams' conduct "was verbally abusive" but "does not rise to the level of a major offense under the Grand Slam Code of Conduct."
After losing the first set to Stosur and facing a break point in the first game of the second, the 13-time major champion hit a forehand and shouted, "Come on!" as Stosur reached down for a backhand. That's when Asderaki ruled that Williams hindered Stosur's ability to complete the point and awarded it to Stosur - putting the Aussi ahead 1-0 in that set.
Williams went over to talk to Asderaki, saying, "I'm not giving her that game."
Williams also said: "I promise you, that's not cool. That's totally not cool."
Some fans began booing, delaying the start of the next game as both players waited for the commotion to subside.
During the changeover two games later, Williams continued to talk to Asderaki, saying, "You're out of control. ... You're a hater, and you're just unattractive inside."
Williams also told Asderaki: "Really, don't even look at me."
Williams was under probation because of an outburst at the 2009 U.S. Open. She was fined $10,500 for that incident.
The Associated Press contributed to this report.