The home ground of London Irish will host the last-four tie, featuring the winners of the Wasps v Exeter and Saracens v Northampton quarter-finals, on Saturday 23 April.
Leicester Tigers will play at the City Ground in Nottingham if they make the last four and face Racing 92.
If they meet Toulon, the game will be at the Allianz Riviera in Nice.
The semi-finals are played at neutral venues designated by the tournament's organisers.
Home-country advantage is awarded depending upon how the club has done in the pool stages and whether a club has won an away quarter-final.
A side ranked first or second in the pool stages will only get a home semi-final if they face the other home quarter-final winner, otherwise they will be away from home.
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The Madejski Stadium in Reading will host the all-English semi-final of this season's European Champions Cup.