Two-dimensional position-sensitive silicon detectors ('matrix detectors') have been designed, procured, and tested as part of the development of the solar isotope spectrometer (SIS) instrument for NASA's Advanced Composition Explorer (ACE) mission. Important characteristics of these devices include: thickness approximately 50 - 90 micrometer, active area 34 cm2, 64 strips on each surface with 1 mm strip pitch. The SIS instrument uses four such detectors, processing signals from each of the 512 individual strips with a separate 12-bit pulse height analyzer implemented with custom-designed VLSI circuits. A set of 25 matrix detectors have been characterized through a variety of tests intended both toe select the best candidates for use in the flight instrument and to provide the calibrations needed to interpret flight data. We discuss the design of the SIS matrix detectors and present selected results from the detector tests that have been performed.