"I feel very good," Cilic said. "Especially in the second set I had to stay mentally focused and play every point. The tiebreak was crucial to keep up the pressure.
"I could see that Kyle's movement was a little restricted, so I tried to move the ball around. I have two days off now. It will be a great final on Sunday."
Halep saved two Kerber match points in dramatic fashion while her opponent did the same in the match lasting for two hours, 20 minutes.
Halep is into her first Melbourne final after losing Roland Garros finals in 2014 and 2017.
"It was a very tough win, I'm shaking now," Halep said. "I'm very emotional. Angie is a tough opponent, she moves so well and is hitting from everywhere.
"I'm glad I could resist."
The Romanian, who was bothered by an ankle injury during the early rounds, credited much of her victory to "confidence in myself."
"I told myself I would fight for every point during this event and then have a big rest afterwards. I tried to be very calm, but today was a roller-coaster, up and down.
"I didn't give up on even one ball. If you don't give up you can win the match in the end. I did that and I'm proud of myself."
Kerber, the 2016 Melbourne trophy-holder, had 33 winners to 50 for Halep, who broke on nine of 22 chances and dropped her own serve seven times.