Fognini, who won his fifth career title in Gstaad, Switzerland on Sunday, received medical treatment for a lower back injury early in the opening set but eased past Thomaz Bellucci 6-3, 6-1. The Brazilian won just one of his eight service games.
The third-seeded Italian plays former champion Kohlschreiber for a place in Saturday's final of the last clay court event of the season.
The German took the last five points of a third-set tiebreaker to outlast Dusan Lajovic of Serbia 4-6, 6-4, 7-6 (5). Last week, Kohlschreiber pulled out of his semifinal in Hamburg with a thigh injury.
Also, 157th-ranked Sebastian Ofner of Austria reached his maiden semifinal by defeating Renzo Olivo of Argentina 6-3, 1-6, 6-3. The wild card entrant will next play Joao Sousa of Portugal, who rallied to beat Gerald Melzer of Austria 2-6, 6-1, 6-3 in a match interrupted by rain.