Kane, who already had two goals and an assist, completed his hat trick when he scored on goalie Jonas Gustavsson at 14:16 of the second period to give Chicago a 6-0 lead.
It was the Blackhawks' fourth goal of the period; they scored three in the first 5:17 and chased Bruins starting goalie Tuukka Rask.
Kane, who leads the NHL in points, has 43 goals and 57 assists this season.