Surkamp joined the club in Toronto, where the White Sox opened a four-game series against the American League East-leading Blue Jays.
The 26-year-old, who was acquired from the Giants via a waiver claim in December, had been excelling with Charlotte as of late, and was named the Triple-A International League Pitcher of the Week for June 16-22.
"It's good to be back," said Surkamp, who was starting at Triple-A but will pitch out of the bullpen for the White Sox. "Hopefully, I can help the team out. We'll see what happens, but I'm ready to pitch."
Surkamp, 4-5 with a 4.54 ERA with Charlotte, has been impressive in the Minors, particularly over his past two starts, during which he allowed only one run over 14 innings.
His strikeout rate at the Triple-A level has risen sharply over the past season. In 2013, he recorded 6.81 strikeouts per nine innings in 11 starts with Fresno, and has seen that rate climb to 10.31 over the same number of starts with Charlotte in 2014.
"I've definitely felt better the last couple of weeks," said Surkamp, who is the club's No. 20 prospect according to MLB.com. "I don't know if I could pinpoint what it is that's changed. That's just how baseball is sometimes. You go through ups and down. I started off slow, but I think I've found a little bit of a groove."
White Sox manager Robin Ventura doesn't expect Surkamp will have to make any adjustments switching to a bullpen role, and stressed his experience as a starter gives the team more length among its relief pitchers.
"At this point, we just needed some length. I think the way it was going for us, we needed something more than a guy just to come in and just get one guy," he said. "With Eric coming up, with what he's been doing, it gives us the length we really need at this point."
Surkamp made his season debut in Thursday night's 7-0 loss to the Blue Jays, allowing one run on one hit over 1 1/3 innings, walking one and striking out one.
Downs, 38, pitched to an 0-2 record and a 6.08 ERA in 38 appearances for the White Sox. He was in his first season with White Sox. He's gone 38-38 with a 3.57 ERA in 602 appearances in the Major Leagues, and he's pitched for the Cubs, Expos, Blue Jays, Angels, Braves and White Sox.
"Scott was a pro and he's good guy to have in there, just with the younger guys that are learning to do stuff in the bullpen " said Ventura. "It just didn't work, being able to just get the one guy. And he was having some [struggles] with righties, and I think in the end, you're looking to giving the younger guy the shot at it and go in and do an inning or two."
Jamie Ross is an associate reporter for MLB.com. This story was not subject to the approval of Major League Baseball or its clubs.