The Belarusian, who was beaten by Leylah Fernandez in the last four 12 months ago, survived a close second set to defeat Czech Pliskova 6-1 7-6 (4).
Sabalenka, who trailed Kaia Kanepi 6-2 5-1 in her second-round match, will bid to reach her first career grand slam final having also lost to Pliskova in the last four at Wimbledon last summer.
The 24-year-old was unable to play at Wimbledon this year because of the ban on Russian and Belarusian players, and used the time to train in Miami.
Having struggled horribly with her serve at the beginning of the year, hitting huge numbers of double faults, Sabalenka appears to have fixed the problem.
Her serve worked very well on Wednesday, with the sixth seed not facing a single break point and hitting three times as many winners as Pliskova.