We report a magnetotransport study of the termination of the spin-resolved integer quantum Hall effect by controlled disorder in a gated GaAs/Al x Ga 1− x As heterostructure. We have found that, for a given Nth Landau level, the difference in filling factors of a pair of spin-split resistivity peaks δ ν N=| ν N↑-ν N↓| changes rapidly from one to zero near a critical density n c. Scaling analysis shows that δ ν 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 the termination of the spin-resolved quantum Hall effect is a phase transition.