An interferometric semiconductor x-ray detection system is proposed in this paper. The system is based on the RadOptic effect, and it utilizes Fabry-Perot interferometry to measure radiation-induced changes in the optical refractive index of a semiconductor (GaAs). In this work, the intrinsic time resolution and the sensitivity of a Fabry-Perot interferometric sensor were systemically studied. Based on the transient free carrier absorption model, the prototype system was established to quantitatively measure the time-dependent x-ray flux with the deconvolution algorithm for the first time. The time resolution of the detection system was approximately 21 ps, and the output signal induced by an x-ray pulse showed a high signal-to-noise ratio and immunity to electromagnetic interference. This interferometer will enable x-ray bang-time and fusion burn-history measurements in inertial confinement fusion with higher time resolution. © 2020 Author(s).