The win guarantees that 25-year-old Florida native Stephens will make her debut in the top 10 when the WTA rankings are released after the tournament.
Tuesday's win was Stephens' second straight triumph over a former world number one after she defeated third-seeded Garbine Muguruza to reach the quarter-finals on Monday.
Stephens said staying consistent was the key to her win over Kerber.
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“When you play a player like Angie you have to execute your game well,” Stephens told reporters. “And then you have to make sure that when you are executing your game you stick with it. Like a lot of times you can venture off and start, you know, doing other things.”
Stephens faced just one break point in reaching her first semi-final since winning the U.S. Open last year.
Kerber, who was playing less than 24 hours after a three-set win over qualifier Wang Yafan that lasted nearly three hours, said her schedule was beginning to take its toll. “I was really feeling a little bit tired today," Kerber said. “I mean, of course it was windy, it was tricky, but I have played so many matches in the last three months that I was feeling it a little bit today in my body."
Azarenka continued her strong run in Miami where she has now won 11 straight dating back to her 2016 title triumph. Azarenka, who broke Pliskova seven times, will be playing in her first semi-final in two years. The former world number one was absent from the game for eight months due to a custody dispute involving her son.
(Reporting by Rory Carroll; Editing by Toby Davis/Peter Rutherford)
