  We report a magnetotransport study of the termination of the spin-resolved
integer quantum Hall effect by controlled disorder in a gated GaAs/AlGaAs
heterostructure. We have found that, for a given N^{th} Landau level, the
difference in filling factors of a pair of spin-split resistivity peaks
\delta\nu_{N}changes rapidly from one to zero near a critical density n_{c}.
Scaling analysis shows that \delta\nu_{N} collapses onto a single curve
independent of N when plotted against the parameter (n-n_{c})/n_{c} for five
Landau levels. The effect of increasing the Zeeman energy is also examined by
tilting the direction of magnetic field relative to the plane of the
two-dimensional electron gas. Our experiment suggests that the termination of
the spin-resolved quantum Hall effect is a phase transition.
