Australia keeper Alyssa Healy led with 77 from 45 balls for the Sixers as they racked up 169-6 from their 20 overs.
Knight was then run out for three by Ireland's Kim Garth as the Hurricanes were bowled out for 66 in 14.1 overs.
The Sixers, runners-up in 2016, face Perth Scorchers in Saturday's final.
That game will be held in Perth, at the Waca - which is dubbed 'The Furnace' for Big Bash matches - as a double-header with the men's final, with the Scorchers having made it to the final of both the men's and women's events.
Knight had led the Hurricanes to the WBBL semis in 2016's inaugural competition, where they were beaten by the Sixers in a rain-affected last-four tie.
England captain Heather Knight was a losing semi-finalist again as her Hobart Hurricanes side were beaten by 103 runs by the Sydney Sixers in the Women's Big Bash League in Brisbane.