Vaughan, who replaced Chris Tarrant in the 95.8 Capital FM breakfast hotseat at the end of March, recorded a reach of 519,000 adults between 6am and 9am.
The survey, which ran for the six months from March 15 to September 12, gives Vaughan 91,000 more listeners than the previous period.
Gfk's figures gives Vaughan 148,000 more listeners a day than closest rival, Jono and Harriet on Heart 106.2 FM.
Magic FM's Graham Dene recorded a reach of 272,000 adults, up 100,000 on the previous period.
Official radio listening results are published by Rajar on Thursday. The Gfk survey is backed by The Wireless Group, the owner of TalkSPORT.
If you have an opinion on this or any other issue raised on Brand Republic, join the debate in the Forum here.