Portugal defeated France 2-0 on Wednesday in Medellin with its stout defense and goalkeeper Mika registering their sixth straight clean sheet in the tournament.
In the other semifinal, Henrique scored twice in the last 10 minutes to lift Brazil to a 2-0 victory over Mexico in Pereira. Henrique has five goals and shares the tournament scoring lead with Alvaro Vazquez of Spain.
Brazil has scored a tournament-best 15 goals so far. Philippe Coutinho and Dudu have three each.
Henrique scored with a header in the 80th minute and then slotted home an 8-yard shot from a cross for an insurance goal.
Saturday's game will come 20 years after the previous Under-20 final between former colony and colonizer, which Portugal won on penalties with a team that boasted Luis Figo, Rui Costa and Joao Pinto.
In the first semifinal, Danilo gave Portugal a 1-0 lead with a leaping header in the 9th minute, and Nelson Oliveira made it 2-0 with a penalty in the 40th. France was in the U-20 semifinals for the first time.
Eric Nunez contributed from Pereira.