This paper presents a reconfigurable successive approximation register (SAR) Analog-to-Digital Converter (ADC) of which the resolution can be scaled from 9 to 12 bits for various inertial MEMS sensor applications. The dual supply voltage skill separating digital and analog voltage is implemented for achieving low power consumption. In addition, level shifter connects the interface between digital and analog domain. 3 bit segmented capacitor array are used to decrease the static error and glitches from MSB switching. In the provided 9 to 12 bits mode, this structure consumes 2.5, 2.8, 3.9 and 9.7 μW and achieve 52.3, 57.7, 63.2 and 68.6 SNDR respectively, resulting in figure of merit (FoM) 148, 88.8, 66.3 and 88.4fJ/conversion-step.