The rate of oxide formation on silicon was investigated by in situ I–V measurements, one after the other within 300 s, and as a result the current or I–V gap was used to compare the relative oxidation rate during pore formation at different anodizing currents. The study was based on the electrochemical etching of p-type silicon using HF electrolyte treated with surfactant to obtain pores with straight walls. The study showed that the rate of oxidation during the formation of macropores, which have straight walls and relatively deep structures, decreases as the pores grow down with time, where it shows that the etching rate decreases as the pores grow deep. However, electropolishing resulted in a relatively high and constant rate of oxide formation with time. These observed properties are related to the expected diffusion limitation of oxide-forming (OH−) molecules, which reach the electrolyte-pore tip while etching occurs. Anodic oxide formation rate at the electrolyte-pore tip, which was created under complex kinetic conditions, depends on the pore structure, pore depth, diffusion rate of oxide-forming species, and anodizing current. The fast I–V method is an advanced approach and can be used to study pore formation mechanisms in different semiconductor materials.