The photoacoustic technique is used largely for the thermal and optical non
-destructive characterization of materials. In this paper we present a new
and alternative method for the measure of thermal conductivity in porous si
licon by considering the photoacoustic response at fixed frequency of sampl
es with the same porosity but different thickness. The analysed samples are
fabricated by etching n-type, 1 Omega cm, 550 mu m thick crystalline silic
on; they have a porosity ranging from 40-70% and thickness from 45-250 mu m
. The measured thermal conductivity is lower than the one reported for crys
talline silicon by two orders of magnitude.