Jack Owens had given Ireland the lead after just five minutes when he crossed, but on the quarter-hour France responded through hooker Quentin Lespiaucq.
Tomas Ramos converted to edge France in front, and he was on target again six minutes later after fly-half Thomas Fortunel went over to make it 14-5.
Ross Byrne and Ramos then exchanged penalties for the two sides before Josh Murphy's try, converted by Byrne brought Ireland back to within two points at the break.
Immediately after half-time Ramos slotted a fine drop goal to stretch the lead back to five and with the two sides only able to manage a penalty apiece after that, France booked their place in Saturday's final against England.
Boher said: "I think it was a very high level game, especially for players at Under-18 level. We saw a lot of movement and intent to play from both sides, a lot of ambition and we saw a few tries which is satisfying.
"It wasn't too tight with lots of strategy, there was spontaneity so there were mistakes and chances taken. We took on a very strong Irish team, they caused a lot of problems at the breakdown and they had a very quick three-quarters line.
"It's only a semi-final though and we know that the toughest test is yet to come. We know what to expect from England, from a physical point of view they are very powerful.
"We saw against Portugal they walked all over them, they are strong in all areas but we have our strengths as well. We have some players who are capable of creating things and the team can work together as well. It's open but it will be very tough."
In the other semi-final England powered past Scotland 25-12, racing into a 25-0 lead before seeing the young Scots mount a spirited comeback.
Fielding a much-changed side from the team which had beaten Portugal 82-8 in the quarter-final, England ran in three tries, with Andrew Hughes, Howard Packman and James Chisholm all scoring.
Fly-half Josh Sharp also chipped in with ten points from the kicking tee while Ruaraidh Smith and Reece Patterson got the Scottish tries.
In the other two games in the elite division Georgia picked up an impressive win over Italy, 17-12, while Portugal were comfortably beaten by Wales 45-0.
France 23 Ireland 18
England 25 Scotland 12
Wales 45 Portugal 0
Georgia 17 Italy 12
France v England
Third place play-off
Ireland v Scotland
Fifth place play-off
Wales v Georgia
Seventh place play-off
Portugal v Italy