Ajax will be playing against French football club Olympique Lyonnais in the Europa League semi-finals, according to UEFA's live blog on the lottery in Nyon. The match will take place on Wednesday, May 3rd at 9:05 p.m. CEST.
The other semi final match will be between RC Celta De Vigo and Manchester United FC on May 4th. The Ajax vs Lyon match was also supposed to happen on May 4th, but as that is a day of remembrance in the Netherlands, Amsterdam asked that it be moved.
Ajax starts with a home match. The return in France is scheduled for Thursday, May 11th.