Winger Holmes set a World Cup record with five tries in last week's quarter-final victory over Samoa in Darwin but went one better at Lang Park as the defending champions cruised into the title decider.
The Kangaroos have been winners or runners-up in all but the first of the 15 World Cups and on this showing will be overwhelming favourites to lift the trophy for the 11th time at the same stadium next Saturday.
"Really pleased with the effort tonight," said Australia skipper Cameron Smith.
"We've just got to throw the ball to Valentine Holmes, he's just scoring left, right and centre - 11 in two matches - we've just got to get it to him again next week."
Australia fullback Billy Slater grabbed his 15th and 16th World Cup tries to better the career record for the tournament he previously shared with Jarryd Hayne, the 12-cap Kangaroo who turned out at stand off for Fiji on Friday night.
Winger Dane Gagai also grabbed a double as the ruthless co-hosts ran in 10 tries to overpower Fiji, who stunned former champions New Zealand in the quarter-finals last weekend.
"It was a tough assignment against Australia," said Fiji captain Kevin Naiqama. "We've finished in the top four in the world, which is a great achievement for us."
England will meet tournament surprise package Tonga in the other semi-final in Auckland on Saturday.
(Reporting by Nick Mulvenney in Sydney; Editing by Jon Boyle)
