Semele was just your average mortal princess. She was the daughter of Cadmus, king of Thebes. She hadn't been the talk of the town until she had an affair with the king of the Gods, Zeus.
The story about this affair is a real shocker. Semele met this man in Thebes and had an affair with him. He told her he was a God and his name was Zeus. She believed him and things would have been fine but you know how some people are. Hera, his wife, didn't like Zeus's many affairs and found out about this one and plotted revenge against Semele and her unborn child.
Semele was rather niave and when Hera came to visit as an old women she let her in and they just got along like old friends exchanging stories. The conversation finally turned toward Zeus and the affair. Semele was in heaven with the way things were going with Zeus and Hera was aware that Semele wasn't the brightest light around so she told Semele how to make Zeus prove he was a God to her and not just an imposter.
Well Semele had to find out if Zeus was telling her the truth so she seduced him and made him promise her anything she asked of him. Zeus of course did and he soon realised he had been cornered into something he didn't want to do. Of course he could of said no and explained why and surely Semele would have understood, but you know how men are.
So not wanting to go back on his word he showed his true form to Semele. Lightning bolts and thunder raging. This of course was to much for Semele to withstand and she was burnt to a crisp. Zeus was sad yet he was able to save his unborn son Dionysus.
The story was told that Zeus put a deep slash in his thigh and this is where he had his fetus placed. The cut was sown up and there is were Dionysus stayed for a few months until he was ready to be born. For this reason he is sometimes referred to as the "twice-born God."
Dionysus was raised by his aunt and uncle for awhile then by nymphs. As he reached adult-hood he wanted to take his place on top of Mount Olympus with the rest of the Gods yet he didn't want to leave his mother behind. Dionysus went to the underworld and managed to have his mother released. Dionysus knew he had to do something to conceal the fact that Semele had been released from the underworld so he could keep jealousy down so he changed his mothers's name to Thyone, which means "Raging Queen" to some and "she who receives the sacrifice" to others.
The two lived out there days on Mount Olympus with Dionysus by Zeus's side as one of the "Twelve Great Ones."
Grant, Michael and John Hazel. Who's Who in Classical Mytholology, Clays Ltd. 1993
Graves, Robert. Greek Myths. Doubleday & Co. 1981
Powell, Barry. Classical Myth. Second Edition. Prentice-Hall, New Jersey. 1998