The photoacoustic technique is a technique that studies the radiation-matter interaction through a well-known phenomenon as photoacoustic effect. In this work using a theoretical fitting of the photoacoustic signal amplitude the effective thermal effusivity of porous silicon samples was determined. The porous samples were obtained by means of photoelectrochemical etching of (100) n-type silicon wafers with different resistivity values, all in the range of 1-25 Ω­ cm. The samples were formed at room temperature in an electrolytic bath composed by a mixture of hydrofluoric acid (48%) and ethanol having a composition ratio of 1:1 in volume under potentiostatic condition (20 V) and an etching time of 2 minutes using back illumination provided by a laser beam with a wavelength of 808nm. The obtained values for the effective thermal effusivity of the porous samples diminished respect to the corresponding value of single-crystalline silicon, this decrease can be attributed to the restriction of the mean free path of phonons in the porous network.