This paper presents a Successive Approximation Register Analog-to-Digital Converter (SAR ADC) design for sensor applications. An energy-saving switching technique is proposed to achieve ultra low power consumption. The measured Signal-to-Noise-and-Distortion Ratio (SNDR) of the ADC is 58.4 dB at 2 MS/s with an ultra-low power consumption of only 6.6 μW from a 0.8V supply, resulting in a Figure-Of-Merit (FOM) of 4.9 fJ/conversion-step. The prototype is fabricated in 65 nm CMOS technology with an area of 0.024 mm².