Chelsea will have to defeat Basel over two legs in order to reach the final of the Europa League.
The West London outfit, who have never faced the Swiss opponents before, will play the first semi-final leg away from home on April 25, with the return fixture at Stamford Bridge the following week.
Chelsea could have faced a semi-final tie closer to home due to Tottenham Hotspur and Newcastle United both competing at the final-eight stage, but neither side could progress into the next phase.
The Blues reached the final four by securing a 5-4 aggregate win over Rubin Kazan, while Basel knocked out Spurs on penalties.
If Chelsea progress, they will face the winner of the second semi-final between Fenerbahce and Benfica.
