The 22-year-old beat his personal best by one hundredth of a second to set a new Norwegian and Nordic record.
Guy Barnea from Israel won the heat with a 24.99 seconds swim in the first semi-final. Four other swimmers performed faster than Solli. The Norwegian clocked a sixth best time with a 25.14 seconds swim over 50 meters.
If Solli is to win a medal, he must swim a couple of tenths faster in the final on Thursday.
Norwegian national team coach Petter Løvberg said to NTB on Tuesday: “The target is that Lavrans will get to the final.”
The swimmer from Bergen outperfomed himself when it was the most needed. In the qualification round earlier on Wednesday he achieved only 25.65 seconds - the 15th best time.
The two other Norwegian swimmers in the Europe Championship on Wednesday, Sverre Næss and Sindri Thor Jakobsson, both went out of the competition after their swims.
Næss became second [number two] in his heat on 200 meters chest with 2,15.82. That was enough for the 25th place. Jakobsson were in action on 200 meters butterfly. He swam in to a second place in his heat with 1,59.80, but was 1.25 seconds away from a place in the semifinale and became number 21 in total.
Norway has only five swimmers at the European Championship. Solli is the only one with a realistic chance to reach a final.