If you believed you he had the set when he checked the flop, then you should have believed that a semi-bluff is a bad idea.

The point of a semibluff is to add the 30 odd percent chance you have of making a flush if he calls, to the 20-40 percent chance that he will fold to your bet. If the percentages add to more than fifty then it's a profitable play in the long run.

The right move, assuming again that you suspected him of having the J, was to take your free card.