If you are going to make a semi-bluff on the flop like you did you have to follow it on the turn with another pottish size bet. Semi-bluffing is done for 2 reasons, to induce a fold, and to enable a bigger pay off when you hit your hand.

When you check down the turn you are completely canceling out your semi-bluff on the flop. Now if you hit your flush, or trips on the river, it is doubtful that a villain will call your suddenly coming to life after a scare card hits. Keep up the aggression on the turn and then play accordingly on the river.