This article describes the design, fabrication and characterization of a 925 GHz planar branch-line hybrid coupler implemented with a suspended stripline on a 3-µm silicon-membrane support structure. This work enables the integration of directional couplers with active devices in balanced-circuit topologies such as sideband separating mixers. A 3dB coupler design, fine-tuned using full-wave electromagnetic simulations, was fabricated with microfabrication techniques, and characterized from 750 GHz to 1100 GHz using a VNA. Measured isolation was better than 15 dB and amplitude balance was better than 1.1 dB over an 18% bandwidth. Electromagnetic simulations of the coupler were in good agreement with scattering-parameter measurements.