Do you have the money to do an additional year? Is money not a problemo?
Do you happen to live nearby one of the universities?
Do you happen to be interested in subject matter that the places you could go to are well regarded for teaching?
Do you have a clear direction for what you want to do as a career? (I thought I did, but didn't, so don't be shy saying no or not quite).
Have you visited UC campuses? where would you live, and how? Would you have to work?
And so on. We can't guess this about you and your needs, but you can.