The progress of oxidation of a porous silicon layer(PSL) was studied by examining the temperature dependence of the oxidation and the infrared absorption spectra. Thick OPSL(oxidized porous silicon layer). which has the same properties as thermal <TEXT>$SiO_{2}$</TEXT> of bulk silicon, is formed in a short time by two steps wet oxidation of PSL at $700^{circ}C$, 1 hr and $1100^{circ}C$, 1 hr. Etching rate, breakdown strength of the OPSL are strongly dependent on the oxidation temperature, oxidation atmosphere. And its breakdown field was ${1MV/cm^-2}$ MV/cm The oxide film stress was determined through curvature measurement using a dial gauge. During oxidation at temperature above $1000^{circ}C$ in dry $O_{2}$, stress on the order of ${10^9}dyne/{cm^2}{-10^10}dyne/{cm^2}$ are generated in the OPSL.