Halep, who saved two match points to win 6-3 4-6 9-7, will now face Caroline Wozniacki in this weekend's final Down Under.
After cruising into a 5-0 advantage in the opening set, breaking each of her opponent's first three service games, Halep was pegged back slightly but still opened up a convincing lead.
Kerber recovered well in the second set, earning breaks in the fifth and ninth games to level up the contest.
Last year's winner led 5-3 in the deciding set but squandered two set points, and two games later it was roles reversed as Halep failed to take her chance.
At the fourth opportunity, though, the Romanian got the job done to set up a meeting with Wozniacki, who beat Elise Mertens in straight sets.
Second seed Wozniacki lost serve just once en route to a 6-3 7-6(2) triumph, though she also had to save two set points during a match that lasted one hour and 40 minutes.