A cagey first round by both fighters saw Campbell defend and counter well, with a solid right hand at the end giving the Brit a 5-2 first-round lead.
The Japanese came forward in the second round and found himself caught by a few counter-attacking lefts from Campbell and the Brit extended his lead to 11-6 by taking the round 6-4.
Campbell refused to defend his lead in the third, landing some good combinations but got his hands up when needed to block Shimizu's inevitable attacks.
The Brit's superior fitness was clear in the second half of the round and he was able to pick off his opponent to take a 20-11 win overall.
Campbell will face John Joe Nevin in tomorrow's final, after the Irishman defeated the favourite Levaro Alvarez in the first semi-final.