The Anti-Meran Gambit can energize your attack against the Semi-Slav Defense. The move 5.Bg5 allows Black to take with 5...dxc4. Your light square Bishop is still blocked in. Black can shore up this pawn with subsequent moves like 6...b5.
Your Bishop will cause problems on g5, pinning the f6-Knight with the Accepted Lines continuing 5.Bg5 dxc4 6.e4 with e5 threatened. A clever theme follows with the e5 pawn attacking the pinned Knight. Black will play 7...h6 and 8...g5 to unpin the Knight albeit loosening the Kingside.
You will not however allow Black to drive your Bishop back like this. You complete the famous maneuver with 9.Nxg5! hxg5 10.Bxg5. The piece sacrifice is merely temporary as the f6-Knight is still pinned and cannot be saved.
Taking stock after 10...Nbd7 11.exf5 you can see that now you are the one with the extra pawn. In addition Black's Kingside is destroyed. Your strong pawn on f6 is cramping his position and he will find it hard to develop properly and castle his King to safety on the Queenside.