London Pulse finished as runners-up to Thunder thanks to a 62-51 win over Nottingham Forest on Sunday.
Olivia Tchine led the way for Pulse with 48 goals while Anya Williams top-scored for Forest with 31.
Pulse’s victory helped them finish on 36 points and move one point above Loughborough, who they leapfrogged into second spot.
Thunder and Pulse will contest the ‘major’ semi-final where the winner progresses directly to the Grand Final.
Third-placed Lightning play fourth-placed Forest in the ‘minor’ semi-final.
The winner of the ‘minor’ semi faces the losing side from the ‘major’ semi for a place in the Grand Final, which takes place on 20 June in Manchester at the Co-op Live arena.
Pulse captain Zara Everitt, who was player of the match against Forest, praised the resilience of her team-mates to beat Forest and secure second.
“It means so much to be in the major semi-final. It’s true to say this has been a more difficult season than last season,” Everitt told Sky Sports.
“We’ve had a few injures and some sticky patches but ultimately have got through to the semis and can’t wait to show what we can do.”