  We systematically measured the Hall effect in the extremely large
magnetoresistance semimetal WTe$_2$. By carefully fitting the Hall resistivity
to a two-band model, the temperature dependencies of the carrier density and
mobility for both electron- and hole-type carriers were determined. We observed
a sudden increase of the hole density below $\sim$160~K, which is likely
associated with the temperature-induced Lifshitz transition reported by a
previous photoemission study. In addition, a more pronounced reduction in
electron density occurs below 50~K, giving rise to comparable electron and hole
densities at low temperature. Our observations indicate a possible electronic
structure change below 50~K, which might be the direct driving force of the
electron-hole ``compensation'' and the extremely large magnetoresistance as
well. Numerical simulations imply that this material is unlikely to be a
perfectly compensated system.

Strongly Correlated Electrons;Materials Science;Superconductivity