Presentation Phobia

I am a software Engineer..I am a very reserved type of person.mostly don't get easily mix up with the people.I have a large extent of public speaking phobia...As a software engineer i need to give many times presentation about the new things that going to develop.but some days before also i get so much tensed by thinking about the presentation I going to give.During presentation I get so much afraid that I start shivering n then it all spoils up my presentation