Finland came into the game, played in Duisburg, Germany, after the break and striker Mikael Forssell wasted a good chance to equalise after an hour.
Two minutes from the end Kazim Kazim broke free on the right wing and crossed for striker Semih to score his first international goal.
Turkey will play Czech Republic, Portugal and Switzerland in Group A at the Euro 2008 finals which start on June 7.