Is a DUI, which was a misdemeaner, considered a criminal conviction? It was a first offense and there was no fine, prison, or license revoked. Attending class was required.

Yes, it is a criminal conviction, but it is also a misdemeanor and not a felony.

But in some states I understand a third DUI can be a felony

In the first time, you are treated as a misdemeanor, but after a repeated practices of DUI, it would be suppose as a criminal conviction or felony charges, as a result you might loose your driving license, heavy charges or in a long term jail. This rule is applied in almost every state of the America and some other countries as well.San Mateo DUI lawyer, is the great experience for me which direct me about what to do when you under the trap of DUI.