We present a low-power, energy efficient 32-bit RISCV microprocessor unit (MCU) in 22 nm FD-SOI. It achieves ultra-low leakage, even at high temperatures, by using an adaptive reverse body biasing (ABB) aware sign-off approach, a low-power optimized physical implementation, and custom SRAM macros with retention mode. We demonstrate the robustness of the chip with measurements over the full industrial temperature range, from - 40°C to 125°C. Our results match the state of the art (SOTA) with 4.8 uW / MHz at 50 MHz in active mode and surpass the SOTA in ultra-low-power retention mode.