We have studied the humidity behavior of thermally carbonized (TC) p+-type porous silicon (PS) samples as a function of carbonization temperature. The Fourier transform infrared (FTIR) spectroscopy and gas adsorption measurements indicate that the bond configuration and structure of thermally carbonized porous silicon surface are highly dependent on carbonization temperature. Moreover, the surface affects on the stability of porous silicon but also significantly on its humidity behavior. The porous silicon samples carbonized at or below 650 degreesC remain hydrophobic, while the temperature of 730 degreesC was high enough to produce a hydrophilic surface. The water sorption rate in thermally carbonized porous silicon samples was quite slow, however, this was interpreted to be mostly a consequence of a thick sample. Hygroscopicity was studied by measuring the weight of the sample under various relative humidity values, and also by using isothermal microcalorimeter (IMC). For humidity sensor purposes, we also studied the effect of water adsorption on electrical parameters of thermally carbonized porous silicon layer. The changes of resistance and capacitance were observed both for hydrophobic and hydrophilic surface. (C) 2003 Elsevier B.V. All rights reserved.