I recently reflected on my parenting after reading an article (can't remember what sorry!) and decided that my DS(3.5) wasn't getting enough proactive positive reinforcement from me, mostly I was reactive - so I made the effort to randomly go find him and say he was playing well and sit and play with him, or go find him and say 'hey do you want to read a book'? He was a bit bewildered a first (to my shame ) but we seem to have less tantrums these days. If he seems to be losing control more often I reassess and try to focus on him more again.

Could you keep a notebook of when he's tantrumming? Maybe you'll notice cues, it could even be something simple like he's hungry or tired or thirsty? (one of mine used to be feral, I'd give him a drink and he'd be fine. Weird)

If it keeps up though, maybe you could ask for a referral to a paed or an occupational therapist - I've heard OT's can be great for helping find strategies for kids to stay calm.