The title compounds are typical III-V and II-VI-type semiconductors, having Zinc-blende-type isomorphous crystal structures. The present work was aimed to obtain reliable electron density distributions experimentally and theoretically by means of the maximum entropy method (MEM) based on X-ray diffraction intensity data and ab initio calculation. From the MEM calculation, the electron density maps were determined to an accuracy of 0.05e/Angstrom (3) in each 0.09 x 0.09 x 0.09 Angstrom (3) pixel at 200 K and ambient for GaAs and CdTe, respectively. An asymmetric charge distribution was clearly observed in the Ga-As bonds in the (1 1 0) plane even in ambient, i.e, an appreciable amount of electrons, being of the order of 0.1 e/Angstrom (3) or less for each Ga ion, are attracted from the Ga ion to the As ion. No obvious asymmetry was observed in the Cd-Te bonds on the other hand.