A high-quality quarter-final tie at the Nature Valley International went Kerber's way as the German won 6-4 6-3 in a battle of the former world number ones.
Romanian Halep, the sixth seed at the tournament, played inspired tennis at times but came up short.
Kerber, the fourth seed, said: "I'm really happy with how I played. To play against Simona is always a tough battle and I know I have to play my best tennis.
"She's a great player who has won so much in the last few years. I was just trying to focus on my game and having another good match on grass.
"I'm really, really happy to be in the semis again."
Unseeded Tunisian Ons Jabeur is the player blocking Kerber's path to the final, after she extended a productive week on the English south coast with a 1-6 7-5 6-3 victory over France's Alize Cornet.
"It'll be another tough match before going to Wimbledon," Kerber said, in a WTA interview.
"We've never played before but I will try to continue how I've played in the last few days."
Czech second seed Karolina Pliskova hurried to victory over Russian Ekaterina Alexandrova, needing just 53 minutes to polish off a 6-2 6-0 win.
Pliskova set up a semi-final against Dutch third seed Kiki Bertens, a 6-4 3-6 6-4 winner over eighth-seeded Belarusian Aryna Sabalenka.