  We report in this letter experimental results that confirm the
two-dimensional nature of the electron systems in monolayer InN quantum wells
embedded in GaN barriers. The electron density and mobility of the
two-dimensional electron system (2DES) in these InN quantum wells are 5x10^{15}
cm^{-2} and 420 cm^2/Vs, respectively. Moreover, the diagonal resistance of the
2DES shows virtually no temperature dependence in a wide temperature range,
indicating the topological nature of the 2DES.
