For future measurements while depth drilling, commercial sensors are required for a temperature range from -40 up to 300 °C. Conventional piezoresistive silicon sensors cannot be used at higher temperatures due to an exponential increase of leakage currents which results in a drop of the bridge voltage. A well-known procedure to expand the temperature range of silicon sensors and to reduce leakage currents is to employ Silicon-On-Insulator (SOI) instead of standard wafer material. Diffused resistors can be operated up to 200 °C, but show the same problems beyond due to leakage of the p-njunction. Our approach is to use p-SOI where resistors as well as interconnects are defined by etching down to the oxide layer. Leakage is suppressed and the temperature dependence of the bridges is very low (TCR = (2.6 ± 0.1) µV/K@1 mA up to 400 °C). The design and process flow will be presented in detail. The characteristics of Wheatstone bridges made of silicon, n-SOI, and p-SOI will be shown for temperatures up to 300 °C. Besides, thermal FEM-simulations will be described revealing the effect of stress between silicon and the silicon-oxide layer during temperature cycling.