This behavior is very common in the dog population, and despite what dog owners may think is a learned behavior and is easily stopped. If your dog has basic obedience then teaching him to stop this very annoying behavior can be achieved in just a few days.

First of all, you will be training him to stop this without using real guests as guinea-pigs. Have a family member of friend work with you by ringing the doorbell (or whatever the signal to your dog that guests are here is) for you. Start your dog off in his collar and leash so that you can exert complete control over him. You will need a pocket full of small treats.

Have your friend ring the doorbell and approach the door with your dog on his leash. You probably want your dog to bark once or twice so this is fine. After a few barks, firmly say "quiet". This will have no initial effect on your dog so immediately say "sit" (this is where basic obedience helps). When your dog sits, offer him a treat. He will not be able to bark and chew at the same time. While he is chewing praise him and repeat "quiet" over and over. After a good few practices, try only giving your dog the treat when he stops barking.

Later move on to not always giving him a treat, until you only give him a treat very occasionally. The basis of this kind of positive reinforcement is that dogs nearly always think it is worth behaving in a certain way if there is any chance of them getting a treat.