Maldonado, 32, is hitting .217 with six home runs this year. The former Gold Glove winner went hitless in 11 at-bats with the Cubs.
Chicago acquired Maldonado from the Kansas City Royals earlier this month.
Maldonado has hit .219 with 57 home runs since debuting in 2011. He hit .231 in 41 games for the Astros last year and played in seven playoff games.
Kemp debuted with the Astros in 2016. He's hit .240 with 14 home runs and 58 RBIs in 239 games.
Houston is 69-39 this season. The first-place Astros have an eight-game lead over the Oakland Athletics in the AL West Division.
Chicago is 56-50 this season. The Cubs trail the first-place St. Louis Cardinals by one game in the NL Central and are tied with the Philadelphia Phillies for the National League's second Wild Card spot.