Hembree's non-guaranteed deal is worth $1,312,500. He had a $581,500 salary this year.
The 29-year-old Hembree went 4-1 with a 4.20 ERA in 67 appearances last season, helping the Red Sox win the World Series. The right-hander made four scoreless appearances in the playoffs covering 4 2/3 innings.
Hembree was selected by San Francisco in the fifth round of the 2010 draft and traded to Boston in the July 2014 deal that moved Jake Peavy to the Giants.
Hembree is 12-5 with a 3.46 ERA in 204 major league appearances, all in relief. He also has 226 strikeouts in 216 career innings.
The Red Sox announced the deal on Friday.