An AlGaAs/GaAs ridge directional coupler electro-optic modulator with a voltage-length (VL) product of only 7.0 V mm (L=3.5 mm, V=2 V) is reported. The low VL product has resulted from the efficient electrode configuration as well as the large overlap between the optical and electrical fields in the waveguides. Propagation loss of 3.4 dB/cm and the measured I-V characteristics confirm that the contributions from the Franz-Keldysh, charge-carrier, and thermal effects are small. To our knowledge, this is the lowest VL product ever reported for an electro-optic directional coupler modulator utilizing the Pockels effect. An extinction ratio of 13 dB was measured for the modulator at 0.83 μm wavelength.