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Lisicki, runner-up at last year's tournament, started strongly but fell apart in the face of an excellent display from the third seed, who claimed a 6-4 6-0 triumph in just under an hour.
German Lisicki struggled with a shoulder injury during her victory over Yaroslava Shvedova in the fourth round, but there was no sign of a recurrence as she raced into a 3-0 lead in the first set.
That was as good as it got for the world number 19, though, as unforced errors and the power of Halep proved to be her downfall, the Romanian winning 12 of the next 13 games.
Halep, losing finalist at the French Open in June, had never progressed beyond the second round before this year's competition, but can now look forward to a last-four clash with Eugenie Bouchard after the Canadian beat Angelique Kerber.
Bouchard's rapid rise continued as she defeated her German opponent 6-3 6-4 in an hour and 15 minutes.
Bouchard also reached the semi-final at the Australian Open and the French Open, where she was beaten by eventual winner Maria Sharapova, and is set to move up to eighth in the WTA rankings as a result of her exploits at the All England Club.
Kerber, a semi-finalist at Wimbledon two years ago, had accounted for Sharapova in the fourth round but came unstuck against the in-form 13th seed Bouchard, who will equal the record highest world ranking for a Canadian woman next week.