The 20-year-old from Carmarthen beat the Scotsman Martin Dziewialtowski 9-1 to earn pounds 19,750. That will turn into pounds 75,000 if he can become the first Welshman for nine years to lift the trophy.
Stevens, the world No 53 who beat the world No 4, Mark Williams, 9-4, needed only 30 minutes to complete his victory.
"The first couple of frames gave me a great deal of confidence and I just went on from there," Stevens said. "I expected a tougher match because Martin is such a tremendous potter. I watched his first game and it was frightening the number of breaks he was knocking in."
However, this latest match came too soon for Dziewialtowski after his last-16 victory over Dean Reynolds. Stevens made the most of his rival's tiredness.
It is Stevens' second ranking semi-final in a row and he hopes to improve on his defeat by John Higgins at Bournemouth last month.
"I owe much of my success to my dad Morrell," he added. "When I was younger he used to drive me all over the country to play in various tournaments and pro-ams. Without him I wouldn't be where I am today."Reuse content