Newport Gwent Dragons back Tyler Morgan, 19, has become the first uncapped player to sign a Welsh rugby dual contract.
Dragons wing Hallam Amos and Scarlets prop Rhodri Jones have also signed.
The trio join Wales captain Sam Warburton and flanker Dan Lydiate on joint deals.
The creation of dual contracts was part of a £60m deal between the Welsh Rugby Union (WRU) and regions over funding and governance of the game in Wales.
All three players have represented Wales Under-20s and will remain with their current regions.
Wales head coach Warren Gatland said the latest deals for "some of our youngest prospects" is another "important step forward" for Welsh rugby.
"The structure we have created means a player's development and welfare is monitored by the national squad management and this will help players realise their full potential," said Gatland.
"National dual contracts will strengthen the game at national and regional level and we would like to thank the regions for their help in this process."
Uncapped Morgan, 19, played in Dragons' dramatic Pro12 festive derby win against Cardiff Blues on Friday.
"I'm a local boy and I'm very happy at the Dragons, so I'm delighted to commit my future to them and to Welsh rugby," he said.
"The contracts allow us to work closely with the national squad management and for me that was a big incentive.
"Being able to get that extra advice and guidance will really benefit me going forward."
Dragons wing Amos, 20, won his one and only cap for Wales against Tonga in November 2013 and was part of Gatland's squad for the 2014 autumn internationals.
"I'm really pleased to have been offered this opportunity and I fully intend to make the most of it," said Amos.
Scarlets tight-head Jones, 22, who featured in the squads for all four of Wales' November Tests, said: "These contracts offer us stability and peace of mind as well as first-class resources to allow players to concentrate on playing.
"The Scarlets have played a huge part in my career so far and I hope I can reward theirs and the WRU's faith in me in the coming seasons."
Jones' deal will boost Scarlets who had already agreed deals with captain and hooker Ken Owens and full-back Liam Williams.
The future of fly-half Rhys Priestland however is not so certain.
Scarlets head coach Wayne Pivac said: "We are pleased to see another of our international players committing his future to the region.
"Rhodri has developed through the development pathway here at the Scarlets and we're pleased to see him staying at the region."