The evolution of ferroelectric domain structure in Remeika-grown BaTiO ₃ crystals under an inhomogeneous electric field has been investigated using piezoresponse force microscopy. The ac imaging bias was found to affect the metastable polarization state and lead to the formation of a web-like domain structure. It is suggested that this behavior is due to the existence of subsurface domains arising in single crystals with a layered structure.