The ancient texts of Judaism generally depict Michael as one of the holy angels of God, in fact, an/the chief angel. And Darrell L. Bock's book Blasphemy and Exaltation in Judaism provides sufficient evidence to buttress this idea on pp. 165-169. He supplies evidence that Michael was generally thought to be an angel (i.e., spirit being).
Interestingly, Michael is called ARXISTRATHGOS in 3 Bar. 11-16. See also TAbr 1:4A; TMos 10:2.