Monolithically integrated 8 x 8 semiconductor optical matrix switches have been successfully fabricated for the first time. They were constructed on GaAs substrates from 64 GaAs/AlGaAs electro-optic directional couplers using a simplified tree architecture. The devices have a chip size of 26.5 x 3 mm2 and a minimum total loss (excluding coupling loss) of 8.7 dB.