All-rounder Simon Bowes was the star man as Staithes claimed a three-wicket win over 2019 champions Filey.
Filey skipper Dave Brannan won the toss and chose to bat first, Callum Ferrie (44), Aaron Howard (36no) and opener Nathan Robson (26) helping them to 146-6.
Bowes bagged stunning figures of 4-9 for Staithes, with Jacob Midgeley and Dan Belsham also taking a wicket each.
Despite losing seven wickets in reply, the efforts of Brad Lewis (46) and Chris Morrison (29) set Staithes up before Bowes finished the game off with an unbeaten 17.
Staithes will meet Nawton Grange after they cruised past Scarborough in the other semi-final encounter.
Grange decided to bat first and that was looking a ropey decision as they posted 112-8, Charlie Allott hitting 39 as Scarborough skipper Pat Roberts claimed 4-17 with a wicket apiece for Charlie Hopper, Sam Carver and Guy Emmett.
However, Wayne Dawson produced a superb spell of 4-8 to ensure Scarborough fell 27 runs short in their reply of 85 all out, only David Snowball, who made 30, and Carver’s 20, troubling the scorers.
Sam Farrow also chipped in with 2-12 while Nick Thornicroft and Tom Croot both took one wicket each.
The final will take place at North Marine Road this Saturday, 12.30pm start.
Great Habton beat Bridlington 2nds by seven wickets in the one of only three fixtures to go be completed outside the Premier Division semi-finals.
Brid were all out for just 75 as Greg Miller made 29 and Steven Pockley 23, Ben Corner and John Lumley taking three wickets each.
Doug Bentley then hit 28 not out to guide Habton to the win.
Ebberston 2nds beat Malton & Old Malton 3rds by seven wickets in Division B.
Alex Biles hit 29 but Malton were restricted to 95-9 from their 30 overs.
Aaron Virr was in form with the ball, claiming 4-14 while George Hardie also impressed with figures of 3-16.
Jacob Warters then hit 36 to help guide Ebberston to the win.
In the only other game across the league schedule to be completed, Bridlington 3rds won by five wickets on the road at Scalby 3rds in Division C.
Scalby were all out for 78 before Brid knocked the total off for the loss of five wickets.