The 30-year-old Samoa international has scored five Premiership tries so far this season.
“We’re delighted that Alapati has agreed to continue being a big part of [our] journey going forward,” head coach Pat Lam told the Bears’ website.
“He’s been a positive influence on and off the field with his experience.”
Lam added: “Alapati consistently shows that he is one of the most dynamic players in the competition and he will be a major asset for us going forward.”
The West Country club are 10th in the table, seven points above bottom side Newcastle Falcons, following promotion last season.