Simon, who has won the Bucharest tournament three times, will face Italian Fabio Fognini in Sunday's title match.
Simon topped his German opponent 7-5, 6-2 before Fognini cruised past Hungarian qualifier Attila Balazs 6-3, 6-1.
"I know that I can play very good here," said Simon. "I know the center court perfectly and I really think I can win this tournament one more time."
Simon's past performance against Fognini is also a reason for confidence. He is 3-0 lifetime against the Italian, who will be in his first ATP final.