Harris qualified for the semi-finals in eighth place with eight points from five races and drew gate three for the first semi-final against Jason Crump, Hans Anderson and Andreas Jonsson.
Harris had an excellent race but could not pip Anderson to win but his second place was enough to book his berth in the final.
The second semi-final was re-run after Chris Holder was excluded and saw Jaroslaw Hampel and Tomas Gollob take the two qualifying places.
Harris, who was looking for his first Grand Prix win since Cardiff 2007, again drew gate and for a few seconds had the lead but Jaroslaw Hampel took control and with Gollob getting past Harris on the last lap, the Cornishman had to settle for third place.
The next round is in Torun in Poland on June 19th and you can see it live on Sky Sports 3 at 6pm.