Mary Berry and Paul Hollywood's bakery reality show collected an audience of 5.6 million (a 23.7% share) at 8pm yesterday for BBC Two.
For the first time, the numbers were higher than BBC One's as Holby City could only draw 5.1m (21.4%) at the same time.
The French-themed semi-final featured Berry and Hollywood picking the three contestants that they wanted to take through to next Tuesday's (October 16) grand final.
The overwhelming success of Bake Off's latest run has earned it a Christmas special and a spinoff series for Hollywood.
It has also been reported that Channel 4 has been trying to poach the show's talent to cash in on the popularity of the food show format.
The Great British Bake Off final airs on Tuesday, October 16 at 8pm on BBC Two.