Signed as a minor league free agent, Benson is 1-1 with a 5.14 ERA in three starts.
The Diamondbacks also placed right-hander Leo Rosales on the 15-day DL with a sprained right foot on Thursday. He's 2-0 with an 8.10 ERA in nine relief appearances.
The Diamondbacks are Benson's third team in the last three seasons. He missed all of 2007 after rotator cuff and elbow surgery, and is 70-75 with a 4.42 ERA in nine seasons.