Two of the most successful teams in the competition met at The Lawn, but once Ireland internationals John Anderson and Stephen Doheny were dismissed, Merrion collapsed from 150 for one to 263 all out, well short of the Villagers 324, dominated by a 150 runs stand between Thompson (88 off 60 balls) and Morgan Topping,
But there was disappointment for Instonians who failed their tough test against The Hills, going down by six wickets after being bowled out for 129 with only Cade Carmichael getting past 30.
Pembroke and Leinster complete the last four line-up.
However, the NCU are assured of a National Cup finalist for the first time since 2014 after all three teams won their quarter-finals yesterday.
Matty McCord took five cheap wickets as Cliftonville Academy bowled out North West Premiership pacesetters Killyclooney for just 76 to end North West interest in the competition after St Johnston’s defeat by Rush.
Meanwhile, Ardmore lost their unbeaten Premiership record to Bready yesterday in a last-over thriller while the Dragons pulled off a remarkable run chase against Typhoons, scoring 290 with 11 balls to spare.