Contactless current measurement based on Hall-effect sensors can be performed in either closed-or open-loop configuration. In this paper an open-loop sensor system with a current-mode output is described. The system measures the magnetic field induced around the current path targeting high linearity, accuracy and speed. As the accuracy of the Hall sensor microsystem is affected by temperature-dependent offset and sensitivity of the sensing element, system-level solutions are developed to minimize these effects. The full system integration represents a design challenge as both voltage and current references are directly involved in the sensitivity calibration and both contribute to the system sensitivity drift. The measurements show a sensitivity drift lower than 80ppm/degrees C, the offset drifts less than 300nT/degrees C and the non-linearity is less than +/- 0.08%. The effects of the varying external field on the calibration loop are analyzed and the theoretical prediction is validated by measurement.