Actually, DUI is a "hybrid" misdemeanor (MM). I say that because it involves less possible jail time that a 1st degree MM (up to 6 months for first offense with no damage or endangerment) but more than a 2nd degree MM. It also provides for probation up to 12 months, which is the outside limit for a 1st.
It is an un-categorized misdemeanor and is technically a second degree misdemeanor. But because it primarily carries First Degree Misdemeanor penalties, it is referred to as a First Degree Misdemeanor for simplicity's sake.