Falkirk manager John Hughes praised Killie and Naismith but claims his players contributed to their own demise.
He said: "We have to give full credit to Kilmarnock. They got the required result and now they are in the final. It's disappointing because with the Old Firm out, we felt we had a chance to win the cup.
"The first goal we lost was poor, our two centre halves went for the same ball and missed it.
"And sometimes I think we try and play too much football, we should have changed it around and played back-to-front football.
"But Naismith was fantastic. I wish I had him in my team and what I like about the guy is that he seems to be down to earth."