Several players will miss the Euro Cup semifinals because they have amassed 2 yellow cards in the first 5 matches.
What would happen if all 23 players had amassed 2 yellow cards? Would the semifinal be a walk over to the other team?
Under the IFAB Law 3.1 - Number of players:
A match may not start or continue if either team has fewer than seven players.
So only 17 players would need to amass 2 yellow cards in order to forfeit the next match. The team with fewer than 7 players would forfeit the match 3 goals in favour of the opposing team (source).
This is possible because all players on the field of play, including substitutes, can be disciplined under Law 12.3 - Disciplinary Action.