Described are the design and characterisation of an ultra-low-power temperature level detector (TLD) and temperature sensor based on a silicon-on-insulator (SOI) CMOS integrated circuit (IC) for harsh environment applications. Since this IC is mainly for harsh environment applications (e.g. high temperatures and radiations), it has been designed and manufactured using the 1m high-temperature SOI-CMOS technology provided by X-FAB. The measured power dissipation of the TLD circuit is 9W at a supply voltage of 5 V and temperature of 27 °C, according to the measurement results of the manufactured design. © 2012 The Institution of Engineering and Technology.