Porous silicon was prepared by an anodic etching. The pore size was about 10 nm at an etching time of 20 sec and a current density of 20 mA/$ extrm{cm}^2$. The porous layer was composed of an micro-porous layer (0.6 ${mu}{ extrm}{m}$) and a macro-porous layer (10 ${mu}{ extrm}{m}$). Room temperature PL with maximum peak 6700$AA$ appeared. The peak disappeared by an oxidation reaction when the porous silicon was heated to 100~20$0^{circ}C$ in atmosphere. In order to avoid the oxidation a heat treatment was done in H2 atmosphere. The micro-pore and Si column, which formed quantum well, were collapsed by the high temperature. The PL maximum peak of heated sample was gradually red-shifted and showed about 300$AA$ red-shift at 50$0^{circ}C$. The intensity of PL was maintained to high temperatures in lower pressures. The porous Si was carbonized in C2H2+H2 gas in order to increase thermal stability. The carbonization of the porous Si prevented red-shift of the maximum PL peak caused by sintering effect at high temperatures, and the carbonized porous Si showed Pl signal at higher temperatures by above 20$0^{circ}C$ than the sample in H2 atmosphere.