The Wimbledon champion sealed a 6-2, 6-4 triumph over the 2017 French Open winner with her 11th ace, her 190kph (120mph) serve proving her most potent weapon.
The Moscow-born Kazakh has delivered 35 aces in reaching the final four, more than any other woman at Melbourne Park.
It was a category she also led when she won her Wimbledon crown last year.
Ominously for her semi-final opponent, Jessica Pegula or Victoria Azarenka, Rybakina said her serve is better now than at Wimbledon.
"I would say that I always served big, but for sure when I started to work with my coach, we did a lot of changes on the technique," the 22nd seed said after taking 1hr 19min on Rod Laver Arena to dismiss Latvia's Ostapenko.
"I gained even more power. It's my weapon on the court and of course we are trying to work on it. Always a lot to improve."
The 23-year-old Rybakina had declared "she could beat anyone" after knocking out top seed Iga Swiatek in straight sets.
Now she is eyeing a second major crown, with only two of the top 10 seeds left in the draw, Pegula (3) and Aryna Sabalenka (5).
"In the beginning it feels like it's such a long tournament," said Rybakina, asked if she thought the finish line was in sight.
"Of course if you keep on winning it seems already close.
"I'm trying to focus just on one match. For sure it's close, that's why everybody is now going to try even harder, fight for every ball. It's going to be tough matches."
Rybakina was quickest out of the blocks, breaking Ostapenko immediately and hammering down three aces to reach 3-1.
She created another break point at 30-40 when a sudden cloudburst halted her momentum.
The players scurried off while the roof was closed and the water mopped up.
After a delay of almost half an hour, Ostapenko saw off the immediate danger.
But she was powerless to prevent the aggressive Rybakina capturing the game on a second break point and she closed out the set in 32 minutes.
- 'Confident' -
Ostapenko upped the power on her groundstrokes at the start of the second, breaking for 2-0 with a scream.
But Rybakina reeled off four games in a row and her 11th ace of the match propelled her through.
She said the experience of already having one major in her trophy cabinet was giving her the belief she could add another.
"Here it's different because, first of all, I already did it once, and of course I got confident that I can do it again," said the world number 25, who would be inside the top 10 had she received points for her Wimbledon win, where Russian and Belarusian players were banned.
After knocking out seventh seed Coco Gauff in the fourth round, the 25-year-old Ostapenko said her confidence was back, but it will have taken a dent after running into Rybakina.
"I'll just try to move forward and try to forget this match as soon as possible," she told reporters.
"I can take only positive things out of here because I feel my game was really good all the matches, except maybe today it was not really there, and she had a good day."