In the ongoing HATNet survey we have detected a giant planet, with radius 1.33 ± 0.06 RJup and mass 1.06 ± 0.12 MJup, transiting the bright (V = 10.5) star GSC 03239–00992. The planet is in a circular orbit with period 3.852985 ± 0.000005 days and midtransit epoch 2,454,035.67575 ± 0.00028 (HJD). The parent star is a late F star with mass 1.29 ± 0.06 M, radius 1.46 ± 0.06 R, Teff ∼ 6570 ± 80 K , [ Fe/H ] = − 0.13 ± 0.08, and age ~2.3+ 0.5−0.7 Gyr. With this radius and mass, HAT-P-6b has somewhat larger radius than theoretically expected. We describe the observations and their analysis to determine physical properties of the HAT-P-6 system, and briefly discuss some implications of this finding.