Semin missed six of the season's first seven games because of a sprained right ankle.
Last season, he was second on the Capitals in goals (38) and points (73), behind only Alexander Ovechkin in both categories, and led the club with 17 power-play goals.
Washington entered Wednesday scoring two goals per game and with an 11.4 percent success rate on power plays, 28th in the 30-team NHL.
"I'm not expecting Alexander Semin just to come walking in here and change our fortunes. It's up to everybody to do the things that we need to do," coach Glen Hanlon said before the game. "Semin will be on the ice for 20 minutes, so he's not going to come in and score five goals. But ... we are expecting some more production off of our power play, and it's going to help having him in there."
The Capitals returned right winger Joe Motzko to AHL Hershey.