The Leicester Tigers scrum-half was joined on the scoresheet by Henry Trinder (2), Carl Fearns (2), George Lowe and Charlie Sharples. Tom Homer added 14 points and Rory Clegg kicked a second-half penalty.
Youngs said: "We were patient and kept the ball and made Samoa work very hard in defence. They had some big boys in their side and we wanted to move them around.
"We just kept on chipping away and keeping the pressure up, and before we knew it we were a couple of tries up.
"Samoa work hard but there were a couple of gaps behind them and we managed to exploit them with our kicking game and that paid off with tries."
England got off to a flier with two tries from Trinder in the first 10 minutes. A break from Luke Eves put Trinder away for the first on the right, Homer converting, then a chip over a ruck from Youngs saw the ball break away from Winston Wilson in the dead-ball area for Trinder to touch down again.
Two Homer penalties established a healthy lead and England exposed some striking weaknesses in the Samoa defence and at the set-piece.
A third try followed a Trinder break as Lowe scorched to the line and any fears about dealing with Samoa's big pack evaporated on the half-hour when they were shoved backwards with Fearns finishing off the pushover try.
Youngs scored the fifth try on the stroke of half-time, following a Fearns break from the base of a five-metre scrum.
Tigers full-back Greig Tonks replaced Homer at half-time but could do nothing as scrum-half Auvasa Falealii grabbed the Samoa score. Then Fearns claimed his second on the hour and Sharples jinked over after a neat switch of play by Dave Lewis to take them past the half-century mark 10 minutes from time.
In Wednesday's semi-final, England will play South Africa who came from behind to beat France 43-27. Defending champions New Zealand are likely to meet Australia in the other half of the draw.
"South Africa will be very physical," said Youngs. "They'll be a big side, well organised, but we beat them last year and there's no reason why we can't beat them this year. We've got a good bunch of boys and I think it'll be a great game."
England Under-20:
15 Tom Homer (London Irish) (Greig Tonks, Leicester Tigers 41min)
14 Charlie Sharples (Gloucester Rugby)
13 Henry Trinder (Gloucester Rugby) (Dave Lewis, Gloucester Rugby 54min)
12 Luke Eves (Bristol Rugby)
11 George Lowe (Harlequins)
10 Rory Clegg (Newcastle Falcons) (Rob Miller, Newcastle Falcons 53)
9 Ben Youngs (Leicester Tigers)
1 Ben Moon (Exeter Chiefs)
2 James Clark (London Irish)
3 Bob Baker (London Wasps)
4 Dan Williams (Gloucester Rugby)
5 Graham Kitchener (Worcester Warriors) (James Gaskell, Sale Sharks 55min)
6 Courtney Lawes (Northampton Saints)
7 Calum Clark (Leeds Carnegie, captain) (Josh Ovens, Bath Rugby 17-23min, 59min)
8 Carl Fearns (Sale Sharks) (Jamie George, Saracens 67min)
Replacement not used: Shaun Knight (Gloucester Rugby)
Scorers: Tries: Trinder 2, Fearns 2, Lowe, Youngs, Sharples. Conversions: Homer 4. Penalties: Homer 2, Clegg.
Samoa U20: Rayhan Laulala; Taupo Sefo (Ivy Leleisiuao 46), Winston Wilson (Leia Saofaiga 35), Iafeata Laau, Tito David Sfia; Ioane Fuaivaa Sefo (Jonathan Malo 35), Auvasa Falealii; Siaosi Otto-Iona (Aoomavaega Malo 61), Steven Savali, Uini Atonio (Viliamu Afatia 61), Vailele Tauloa, Ray Pese, Lemalu Faatiga, Falemiga Selesele (Mark Faasii 46), Tau Mataafa (John Totini 51).
Scorers: Try: Falealii.Conversion: Laulala.
Yellow card: Saofaiga 69min.
