The semi-finals are 2 legs so surely 4. last 16-8-4
No they aren't.
From the EFL Trophy regulationsSemi Finals.
The four winners from the quarter-finals will contest the semi-finals.
Semi-final pairings are determined by means of an unseeded draw with no regionalisation. .
The Club drawn first is the Home Club.
Matches will be played by way of only one leg and be of ninety minutes duration with no extra time. If the scores are level at the end of the Match then the winners shall be determined by the taking of kicks from the penalty mark in accordance with procedures as approved by IFAB.
I`m certain it`s been over 2 legs in the past, they must have changed it.