Light emitting porous silicon (LEPSi) was prepared by hydrothermal etching of p-type single-crystal silicon. This sample preparation, which does not involve electrochemical etching followed by a rapid thermal oxidation (RTO) process in a dry oxygen ambient, yields blue light emission, the wavelength of the photoluminescence (PL) band peaking at 430 nm. The blue-emission porous silicon (PS) with high mechanical hardness is easily obtained by this technique. Our results are interpreted in terms of the currently suggested theories.