An estimated 24 million Americans watched Fox News Channel's prime-time debate with the top 10 Republican presidential candidates, the highest-rated broadcast in the network's history.
Thursday's debate ratings more than doubled Fox News's best ratings in the past, for election night 2012, the Nielsen company said. A debate with seven lower-polling candidates earlier in the day had 6.1 million viewers.
The debate turned into a slugfest, with front-runner Donald Trump in particular feeling the heat.
He tweeted out criticism of the network's three moderators as "not very good or professional" and retweeted a message from a supporter who called the network's Megyn Kelly a "bimbo".
Fox News chairman Roger Ailes defended his moderators, calling them "the best political debate team ever put on television".