Phase shift measurements of a Schottky-biased, optically controlled coplanar waveguide (CPW) phase-shifter are presented. A prototype device consisting of a CPW atop a lightly doped GaAs epilayer on a semi-insulating GaAs substrate was fabricated and tested. The highest phase shift obtained with an illuminating optical intensity of 4mW/cm2 was 120° at 40GHz for a 1 cm-long device.