The theoretical analysis and direct experiments with samples based on n- and p-type porous silicon demonstrate that porous silicon becomes a piezoelectric because of the reduction of the symmetry of the crystal lattice. It is shown that both n and p types of porous silicon have piezoelectric properties. The piezoelectric properties of n-type porous silicon are 2.5 times weaker than the piezoelectric properties of p-type porous silicon at the same porosity because pores in p-type silicon become wider and smoother with an increase in the distance from the surface, whereas pores in n-type porous silicon become narrower and more sinuous.