France Under-20 ran in five tries to Wales Under-20s' single effort by Luke Morgan at Eirias Park, Colwyn Bay.
The visitors led throughout after scrum-halfEric Escande's early penalty and were 24-6 ahead at the break.
Jefferson Poirot, Julien Kazubek, and Escande ran in first-half tries while Bastien Fuster and Darly Donvo added two more after the break.
Morgan's try was the Welsh highlight and fly-half Sam Davies kicked three penalties and a conversion.
Wales U20 coach Danny Wilson was forced into nine changes after their 30-23 win over Italy at the same venue seven days earlier.
And after their Six Nations campaign ended in defeat by France, Wilson admitted: "They [France U20] showed far better basic skills."
Wales ended the tournament with two wins - against Italy and Scotland - and defeats by England U20 and Ireland U20.
Wilson will have 12 more players available for the Junior World Championships in South Africa in June as the demands of competive leagues will be over by that time.
Wales U20: Ross Jones (Ospreys), Iolo Evans (Scarlets), Luke Williams (Bridgend RFC), Owen Williams (Scarlets), Luke Morgan (Ospreys), Sam Davies (Ospreys), Jonathan Evans (Dragons), Rob Evans (Scarlets), Kirby Myhill (Captain) (Scarlets), Samson Lee (Scarlets), Jack Jones (Ospreys), Matthew Screech (Blues), Ieuan Jones (Dragons), Dan Baker (Ospreys), Dan Thomas (Scarlets).
Replacements: Darran Harris (Blues), Thomas Davies (Blues), WillGriff John (Blues), Carwyn Jones (Scarlets Academy), Reuben Tucker (Blues), Rhodri Williams (Scarlets), Jordan Williams (Scarlets), Cory Allen (Blues).
France U20: Theo Platon; Bastien Fuster, Jimmy Yobo, Jonathan Danty, Yohann Artru; Enzo Selponi, Eric Escande; Jefferson Poirot, Christopher Tolofua, Pascal Cotet, Bastien Chalureau, Andrew Chauveau, Julien Kazubek, Karl Chateau, Kelian Galletier.
Replacements: Jean-Charles Fidinde, Florian Fresia, Kevin Goze, Paul Jedrasiak, Tom Ecochard, Ilian Perraux, Darly Domvo, Stéphane Onambele Mbarga.