Amos, Scott Williams and halfback Rhys Webb all won starts on the back of strong showings in last week's 13-7 win over Georgia.
Gatland has stuck with rising flankers Josh Navidi and Aaron Shingler over experienced pair Justin Tipuric and Dan Lydiate.
Five of the starting side were involved in this year's drawn series between the British and Irish Lions and New Zealand.
Captain Alun Wyn Jones, who will play his 121st Test at lock, and No.8 Toby Faletau started all three Lions Tests. Halfpenny, Webb and hooker Ken Owens had bench roles.
"It's great to name an unchanged pack from the Australia match," Gatand said.
"We were pleased with a lot of aspects of our second half performance in that match so we are looking to build on that on Saturday.
"We have a couple of injuries in the backline but we also have players on form starting. (Wingers) Steff Evans and Hallam Amos are both on form and we are excited to see what they can do."
Wales: Leigh Halfpenny, Hallam Amos, Scott Williams, Owen Williams, Steff Evans, DanBiggar, Rhys Webb; Taulupe Faletau, Josh Navidi, Aaron Shingler, Alun Wyn Jones (captain), Jake Ball, Tomas Francis, Ken Owens, Rob Evans. Reserves: Kristian Dacey, Wyn Jones, Leon Brown, Cory Hill, Justin Tipuric, Gareth Davies, Rhys Priestland, Jamie Roberts.