Studies of long-range electron transport in porous semiconductors have shown that the effective mobility is strongly reduced with respect to that of single-crystalline bulk semiconductors. This strong attenuation of electron transport has been attributed to multiple trapping/detrapping in states located at the internal surface of the porous solid. Here we report microwave reflectivity measurements on a dark and illuminated macroporous GaP network which allow us to probe the trap-free mobility of electrons present inside the core of the network. We obtain the imaginary and real components of the dielectric constant, and the changes of these variables as a function of the incident light intensity. We show that the changes in the real and imaginary parts of the dielectric constant as a function of the light intensity are correlated, and can be interpreted on the basis of a hydrodynamic model. We find that the short-range electron mobility is 3 cm 2 /V s. We compare this value with the mobility obtained from Hall-measurements on single crystals and the effective mobility characterizing long-range transport through a porous GaP network. The transient changes in the dielectric constant upon switching the light on and off reflect the dynamics of electron-hole photogeneration and bulk and surface recombination in the porous GaP network.