Stratford edged out Wymondham 4-3 while Burton beat Lutterworth 3-1 before Leicester Tigers’ Guinness Premiership game against Worcester Warriors on Saturday.
The sides will return to Welford Road for the final, which will be played before Tigers’ next home game against Gloucester on Saturday, March 7.
Two coach loads of supporters made the journey from Burton to cheer on their under-10s team.
Head coach Adam Willetts said: “It was absolutely excellent. Lutterworth were a cracking side and it was our defence that kept us in it.
“I can’t praise the kids enough. They have worked hard and trained hard for this. It means a lot to the parents, we had two coaches of family and supporters here. We have been well supported by the club as well and a lot of thanks go to them.
“I said to them before the game that they are playing on a pitch where world champions have played. Every rugby player would give his back teeth to play at Welford Road and these have done twice already and are coming back for a third time – and they are not even 10! It’s absolutely fantastic.”
Norton Bloomfield, the Stratford Under-10s head coach, was also full of praise for his players following their win against Wymondham.
He said: “It was a thrilling game and went right down to the wire. They are one of the best teams we have played all season.
“Our guys kept on going. They showed discipline and kept a clear head and went through.
“They have really enjoyed the experience of playing on the first-team pitch and are looking forward to the next occasion.”
Kevin Jones, Lutterworth Under-10s head coach, said it had been a “great achievement” to reach the last four of a competition that attracted entrants from across the country.
Jones said: "The players are very disappointed to lose. They have had a great time in this competition. To get as far as we have done has been a great achievement.
"They have made us very proud of them in the way that they have played and conducted themselves.
"They have played at Welford Road on three occasions now and it's always a great atmosphere.
“The game could have gone either way but the best of luck to Burton, they are a very good team and played well.”
Wymondham travelled up to Leicester the night before the game and held a practice session on Nelson Mandela Park, Tigers former training ground, on the morning.
Dominic Findlay, Wymondham Under-10s head coach, said: “The lads are very disappointed to lose, they don’t feel that they played to their best.
“They have had a really good time. We didn’t expect to get this far in the competition. We are disappointed to lose but overall we have to be happy with how well we have done.”
Scott Clarke, Tigers community manager, said: “The semi-finals saw some thrilling and very competitive rugby. All four sides should take huge credit for the way they have played and conducted themselves in this season’s competition.”
The Prima Tiger Cup, which is supported by Loughborough-based Prima Solutions, is now in its 15th season and is open to under-10s teams from across the country.
More than 50 sides entered this year's competition, which began with local festivals at Stoke RFC in Staffordshire, Kenilworth RFC in Warwickshire, Swaffham RFC in Norfolk, Nottingham Boots Corsairs RFC and at Market Harborough RFC in Leicestershire.
More information on the Prima Tiger Cup is available from Leicester Tigers on 08701 28 34 30.
