Piezoelectric crystals have shown promising results as acoustic emission sensors, but are often hindered by the loss of electric properties above temperatures in the 500-700°C range. Yttrium calcium oxyborate, (YCOB), however, is a promising high temperature piezoelectric material due to its high resistivity at high temperatures and its relatively stable electromechanical and piezoelectric properties across a broad temperature range. In this paper, a piezoelectric acoustic emission sensor was designed, fabricated, and tested for use in high temperature applications using a YCOB single crystal. An acoustic wave was generated by a Hsu-Nielsen source on a stainless steel bar, which then propagated through the substrate into a furnace where the YCOB acoustic emission sensor is located. Charge output of the YCOB sensor was collected using a lock-in charge amplifier. The sensitivity of the YCOB sensor was found to have small to no degradation with increasing temperature up to 1000°C. This oxyborate crystal showed the ability to detect zero order symmetric and antisymmetric modes, as well as distinguishable first order antisymmetric modes at elevated temperatures up to 1000°C.