In this paper we present for the first time results of the application of the modulated photothermal reflectance technique to porous silicon (PS) samples with various degrees of porosity obtained by means of electrochemical dissolution of p(-) and p(+) c-Si substrates. Frequency scans yield results which are strongly related to the thermal conductivity, carrier lifetime and surface recombination velocity of PS. A model accounting for these effects has been developed in order to yield a quantitative evaluation of parameters which are of capital importance in both the physics and technology of PS.