They hanged Haman on the gallows he had prepared for Mordecai. Then the king's anger subsided.
Esther 7:10 In-Context
Just as the king returned from the palace garden to the banquet hall, Haman was falling on the couch where Esther was reclining. The king exclaimed, “Will he even molest the queen while she is with me in the house?” As soon as the word left the king’s mouth, they covered Haman’s face.
Then Harbona, one of the eunuchs attending the king, said, “A pole reaching to a height of fifty cubits stands by Haman’s house. He had it set up for Mordecai, who spoke up to help the king.” The king said, “Impale him on it!”
So they impaled Haman on the pole he had set up for Mordecai. Then the king’s fury subsided.