Wycombe Wanderers will play Fleetwood Town in the other semi final.
The regular season in League One and League Two is over after clubs voted by an overwhelming margin to cut the season short due to the coronavirus pandemic.
Clubs opted to use a framework for ending the season put forward by the English Football League board, which meant the final table would be calculated using an unweighted points-per game basis.
The framework retained promotion, relegation and the traditional four-team play-offs.
As a result, Coventry and Rotherham have been promoted to the Championship, while Wycombe, Oxford, Portsmouth and Fleetwood will contest the play-offs, with the dates for those matches to be fixed in due course.
Oxford United boss Karl Robinson said: "We have never wavered in our belief that the season needed to end on the pitch and now we get a chance to finish all the hard work that we started back in July. Whatever happens we have had a season none of us is ever going to forget: there have been some amazing wins, two cup runs and to think that we finished the regular season with the drama of that win at Shrewsbury sums up the way our whole season has gone.
"We’ve trained well over the last couple of days and now we have clarity on the way ahead of us and can take training to the next level as we prepare to play again."
Meanwhile, Tranmere - who had proposed an alternative framework to the one chosen by the clubs - have been relegated to League Two, along with Southend and Bolton.
Swindon, Crewe and Plymouth have been promoted to League One, while Cheltenham, Exeter, Colchester and Northampton will contest the play-offs, with the first legs of the semi-finals taking place next week.
As things stand, Stevenage will be relegated to the National League but Macclesfield could yet finish bottom if they incur further points deductions for alleged breaches of EFL regulations.