An RTP system with accurate lamp power control was used to study the repeatability of Sens Array type “1530” and “1501” thermocouple (TC) wafers. The drift of the “1530” wafers was measured over 200 heating cycles of 20 seconds at 1050 °C and 1150 °C. Over the 200 cycles at 1150 °C, a drift between -0.5 and +1.0 °C was found. Over the 1050 °C cycles a larger drift between +1.0 °C and +2.0 °C was found, possibly caused by the formation of “haze” over the wafer that changed the optical properties of the wafer. Experiments were conducted for the effect of unloading/loading of the wafer in the oven. An instability of maximum ±0.4 °C was found for “1530”, caused by the unloading/loading. The relative accuracy of “1530” from one thermocouple to another shows a typical variation of ±1.0 °C or smaller. The older technology TC wafers (1501), showed considerably higher instability upon wafer unloading/loading and higher TC to TC variations (± 5 °C). The useful lifetime of a TC wafer is at least 50 to 200 heating cycles.