In this paper, techniques for controlling the growth of the bottom oxide formed by simple electrochemical oxidation of porous Si films were explored and the resulting porous silicon-on-oxide structures were characterized. The thickness, uniformity, and density of the bottom oxide layer can be adjusted by selecting the porous silicon morphology and controlling the conditions of oxide formation. In particular, very uniform interfaces between the oxide layer and a porous silicon overlayer were obtained in multi-texture porous silicon samples.