As his age, it might very well be a psychological problem and you could spin your wheels forever trying to figure it out on your own. Our daughter was prone to explosions several times a day. It was terrible and disruptive to the whole family. Then, when she started first grade, OCD behaviors developed. We took her first to therpay and then to a psychologist at Children's. She was diagnosed with OCD, high anxiety, innate perfectionism and sensory integration disorder. She is in fourth grade now, on medication and doing wonderfully. She have found the happy, social girl who was smothered by that mess of anxiety. Often, these behaviors don't present until they start school and have to spend the whole day trying to fit in and meet expectations. An evaluation couldn't hurt.
We have experienced this and there is a solution. Tantrums can be a form of control so the control has to be reversed through negative practice. This is not for everybody but it worked fast for us. Few words are better and actions should be swift. There should be no spanking. He must be told that he cannot behave this way in the main area of your home. Simply carry child to his room and before closing the door calmly tell them to let you know when he is done, then stand outside the door quietly and wait. You may have to hold the door closed to keep him from trying to run out and through the house. When he tells you he is done you get down on his level and ask, " are you sure?" You then tell him, "I don't think you are done and see more tantrum in you, so I need you to throw another one while I wait outside your door and when I think you are done I will open the door." After a few days of this you will see a big change because you now control the tantrums so he will no longer need to throw them.
It is imporatnt at this age that you exercise your jurisdiction with him and that he not perceive that 'it's his way or the highway'. Take a look at Lynn Clark's book SOS Help for Parents. You'll recognize a lot of what your son is doing. Follow Clark's guidelines and you'll see improvement in this behavior problem.
Thats a tough one. My oldest daughter was like that. I took her to the doctor to find out if something was wrong with her. He told me she was spoiled. I basically dealt with it until she grew out of it. It's hard though because the school was always on my back. By the time she was in first grade she was better.