Halep, at No. 5 the only seed remaining in the tournament, easily got by Medina Garrigues 6-2, 6-1. She didn't face a break point while breaking Medina Garrigues' serve five times.
Her semifinal opponent Friday will be Kiki Bertens, who defeated Garbine Muguruza Blanco 6-1, 6-4 in a battle of qualifiers. Bertens had six breaks in nine receiving games and won 56 percent of the points when receiving serve.
Mathilde Johansson upset third-seeded Petra Cetkovska. Johansson dropped her serve four times but had six breaks and won 58 percent of the points when Cetkovska served. Cetkovska also committed 10 double faults.
Laura Pous-Tio earned her semifinal spot with a 6-4, 6-1 win over Irina-Camelia Begu. Pous-Tio lost only 14 points in her eight service games.
Halep won her only previous match against Bertens while Pous-Tio and Johansson have never played each other before.
None of the four semifinalists have won a WTA tournament.