  We report thermoelectric measurements of the low carrier heavy fermion
compound URu2Si2 at high fields up to 34T and at low temperatures down to
500mK. The field dependence of the thermoelectric power (TEP) and the Nernst
signal shows successive anomalies deep inside the hidden order (HO) phase. The
field position of these anomalies correspond to different changes in the
Shubnikov-de Haas frequencies and effective masses around 12 T, 17 T, 23 T and
30 T. These results indicate successive reconstructions of the Fermi surface,
which imply electronic phase transitions well within the HO phase.
