We investigated the spatial distribution of densely contact-electrified electrons on a silicon oxide layer in air with a modified AFM. From the observed full width at half-maximum (FWHM) and the peak value, we found that the spatial stable-unstable phase transition occurs. We also found, for the first time, that an unstable state exists around the stable state, and that the boundary of the stable state collapses into the unstable state. We also found that the stable state turns into the unstable state by a spatial phase transition and subsequently into the trapped state.