  Possible existence of "hot-sector generations" above the well known 3
generation bound is investigated on the basis of a model of leptons and quarks,
which is based on the Harari and Shupe's one. Our model predicts the existence
of {\bf3 + 1} generations above the ordinary "cold-sector" 3 generations.
Majorana neutrinos are introduced to realize the heavy neutrino masses in
hot-sector generations. Properties of heavy neutrinos are also discussed.
