Bulk and porous membranes of gallium phosphide have been characterized by o
ptical second harmonic generation (SHG) technique using a 1064 nm pump beam
. The porous membranes prove to exhibit an enhanced SHG in comparison with
the bulk material. Taking into account the porosity-induced anisotropy we s
how analytically that the phase matching conditions can be fulfilled for me
mbranes possessing a degree of porosity higher than 30%.