The European champions face the co-hosts in front of what promises to be a packed and hostile crowd at the 80,000-capacity Stadium Australia.
There is a long-standing sporting rivalry between England and Australia and neither side has ever reached the final of the Women's World Cup.
England know the benefits of having a bumper crowd in their corner, having won the European Championship last summer on home soil.
But the Lionesses and Barcelona's Walsh are now on enemy territory.
"When you have the crowd behind you it gives you that extra push," said the 26-year-old, who was stretchered off earlier in the tournament with a knee injury but is now back in Sarina Wiegman's side.
"But I also think that when you are playing against it, when you can quieten the crowd, it's also a very nice feeling.
"Maybe trying to take the momentum out of (their) game is going to be important.
"So there's positives and negatives to both and I've experienced both," she told reporters.
Walsh said she was aware of talk among fans and media about the rivalry between England and Australia but she is more interested in reaching the final and winning the World Cup.
"For us, it is a semifinal, it is a massive game, regardless of who you are playing," she said.
"We are all just really focused. A lot of us aren't really on social media, we are not listening to what's going on outside.
"That's what has got us this far at this tournament."
England are into their third semifinal in a row at the tournament but have never got farther, something Walsh is desperate to fix.
"It is every footballer's dream to play at a World Cup final so for us that's the aim and we hope we can get the job done on Wednesday."
England came into the World Cup as one of the favorites and, having squeezed past Nigeria on penalties in the last 16, they defeated Colombia 2-1 on Saturday to make the last four.
Australia reached their first World Cup semifinal 7-6 on penalties against France.
The Matildas beat England 2-0 away in April to bring the Lionesses' 30-match unbeaten run to an end.