Boyd had denied a Football Association charge over the incident, which happened after a failed penalty appeal during the second half of Hull's 2-0 defeat at the weekend.
But an Independent Regulatory Commission found the charge proven, and his suspension will begin immediately.
That means Steve Bruce will be without Boyd for games against West Brom, West Ham and Stoke - all potential rivals in Hull's fight against relegation.
Bruce defended his player in the aftermath of Saturday's game, saying: "He has tried to talk and shout and something's come out. That's what I've seen of it.
"George Boyd wouldn't do that, no chance. Not deliberately, anyway. He is as honest as they come - he was playing non-league six years ago."