In the silicon-on-nothing (SON), which forms a self-assembled cavity through annealing at a high temperature of 1150°C or higher after forming a periodic anisotropic structure on the surface of a silicon wafer, the initial pattern and final cavity shape after completion of the annealing process are reported only. Therefore, it was not possible to experimentally derive the change of the structure with time when forming the cavity. In this study, the changes in the dimensions of the silicon structure are directly measured through the analysis of the surface of the self-assembled cavity shape over time, and ultimately, the internal cavity change is to be predicted. To this end, a silicon wafer patterned in an array of an anisotropic concave structure having a diameter to depth ratio of 1:7 in a vacuum furnace at a temperature of 1150°C was annealed for various times, and then surface analysis was performed. Through the analysis of the surface and cross-section of the annealed silicon specimen, the change of the characteristic dimensions with processing time was identified.