The 24-year-old had made the quarter-finals at each of the other three Grand Slams and completed the set when she beat 2008 champion Maria Sharapova in the fourth round on Monday.
By contrast, 11th seed Halep had achieved her best Grand Slam result in making the last eight at Melbourne Park and Cibulkova sensed her Romanian opponent would be battling nerves.
"I think it was also important today because I already was on the stage," Cibulkova said.
"I already played couple quarter-finals in the Grand Slam (and) I already did semi-finals in a Grand Slam," she added of her loss to Dinara Safina at the French Open in 2009.
"So that was my experience today. I was ready for it. It was for me like every other match so I didn't take it ... too serious (and) put myself under pressure."
Cibulkova, one of the shorter players on the WTA Tour at 1.61-metres tall (5'3"), used that relaxed approach to play her natural game, which is based on quick feet and deceptively powerful ground strokes.
The 20th seed also attacked Halep's serve and controlled many of the rallies by keeping the Romanian pinned deep behind the baseline.
"I knew I have to be aggressive," Cibulkova said of her game plan for the counter-punching Halep.
"Even if you play well, you play fast, she's there at the ball ... I knew I had to step into the court and play a lot to her weaknesses, use my backhand down the line that she was not expecting, to play some (unexpected) shots.
"When I play my great tennis, I'm really aggressive ... that's what I do the best."
Cibulkova's aggression and risk-taking paid off as she broke early in both sets and used that advantage to put pressure on Halep, who admitted to being a bag of nerves before the match.
"I had emotions, big emotions, and I couldn't manage," Halep said. "Before the match I was very nervous and I didn't feel the ball at all. I couldn't move my body and I couldn't play.
"It feels like I didn't prepare the match very good, and my mind was very down before the match. I couldn't stay relaxed on court."
Cibulkova, who will meet fifth-seed Agnieszka Radwanska for a place in Saturday's final, was unconcerned about the pressure of the semi-final, preferring to take it as she comes.
"Nothing is easy. There is pressure you can feel from everywhere ... so I still want to do the same thing what I came into the tournament.
"I want to really enjoy it. I want to play my tennis. That's when I play my best."
5-Agnieszka Radwanska (Poland) beat 2-Victoria Azarenka (Belarus) 6-1 5-7 6-0
20-Dominika Cibulkova (Slovakia) beat 11-Simona Halep (Romania) 6-3 6-0