This paper reports on a robust technique for the measurement of temperature at multiple heights (levels). This technique uses a bank of straight ultrasonic waveguide temperature sensors attached to a single ultrasonic pulser-receiver instrument. Since the ultrasonic waveguide does not use a junction, the robustness of the sensor is expected to be more for field applications. The measurements have been made by using the L(0,1) ultrasonic guided wave mode end reflection as the signal of interest. The changes in the time-of-flight (DTOF) of this signal as the measurement were related to the local changes temperature of the surrounding medium. Several waveguide configurations were studied and the thickness of the waveguide was optimized to provide a reliable calibration curve. Data was collected and analyzed in a laboratory furnace from 45°C to 1100°C, and the multi-level temperature measurement was demonstrated both in the laboratory as well as in a waste treatment vitrification facility. © 2014 Elsevier Ltd. All rights reserved.