An energy-harvesting wireless sensor node (WSN) integrates a 14-nm, 0.79-mm(2), 32-b Intel Architecture core-based near-threshold voltage (NTV) microcontroller (MCU) that provides 17-mu W/MHz always-ON, always-sensing (AOAS) capability. The MCU implements four independent voltage-frequency islands, managed by an integrated power management unit and features a subthreshold voltage capable on-die oscillator and 42-nm fin-pitch, 8.3-pA leakage-per-bit SRAM. The MCU operates across a wide frequency (voltage) range from 297 MHz (1 V) to 0.5 MHz (308 mV), dissipating 23.5 mW to 21 mu W, and achieves 4.8x better energy efficiency at an optimum supply voltage (VOPT) of 370 mV, 3.5 MHz, and 17 pJ/cycle. A functional AOAS WSN incorporating the NTV MCU shows promise for sustained mu W operation.