Giorgi, belying her ranking of 100th in the world, beat U.S. Open champion Sloane Stephens in the first round and then ousted twice Wimbledon and former Sydney champion Petra Kvitova.
She is yet to drop a set over six matches in qualifying or the main draw and will next meet world number 22 Kerber who staged a 6-3 6-1 victory over Dominika Cibulkova in the last eight.
Former world number one Kerber fell out of the top 20 last year but has made a strong start to the year ahead of next week's Australian Open with victories over Lucie Safarova and Venus Williams this week.
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"I'm not looking back 2017 any more," Kerber, who won the Australian Open and the U.S. Open titles in 2016, said.
"I've had a great off-season and I'm working hard. I'm trying to do my best on court and win as many matches before going to Melbourne.
"It's just the beginning of the year. I'm trying to play my game again, enjoy every minute on court. I'm trying to be aggressive and play like I did the year before last."
The other semi-final in Sydney will be an all-Australian affair between Ashleigh Barty and Daria Gavrilova.
Barty completed a confident 6-3 6-2 victory over Czech Barbora Strycova, while Gavrilova advanced after her last-eight opponent Garbine Muguruza withdrew due to a leg injury.
"I think it's amazing for Sydney and for Australian tennis – we're gonna have an Aussie in the final, which is awesome," Barty said after her win at the Ken Rosewall Arena.
"Dash and I know each other very well so hopefully we can play some good tennis."
(Reporting by Sudipto Ganguly in Mumbai; editing by Pritha Sarkar)
