Lee Brook (two), Jamie Ingham (two) and Jamie Beever led Thornhill to victory and they now meet Gate in the last four on Saturday.
There is also the prospect of a Callaghan Cup final derby as Battyeford Wasps meet Morley Cricket and Sports in the other semi, which has been put back to April 30.
Wilton eased their relegation worries in the Premier Division after they edged a nine-goal thriller against Woodman. Victory saw Wilton move up to seventh place, a point behind Woodman and one clear of Battyeford.
James Goodall and James Blane hit a brace apiece for Woodman but it wasn’t enough to prevent defeat.
Howard Jessop netted the only goal as Battyeford edged out Gate, who are ninth, a point behind Dewsbury Rangers with a game in hand.
Rangers were unable to do title-chasing Thornhill a favour for although Rob Smith found the net, they lost 4-1 at home to Rose and Crown Darton. Rose and Crown jumped above Thornhill on goal difference to go top but they have played two games more.
Dodworth Miners Welfare still harbour title hopes as they are three points behind Thornhill, having played the same number of games.