This work presents a power-efficient wireless sensor implemented using microelectromechanical system (MEMS)-based dry electrodes (MDE) and a ZigBee protocol chip for physiological signal acquisition. To improve signal quality with low electrode-skin interface impedance, a silicon-based MDE is fabricated via micromachining technology. The proposed wireless sensor can provide four different channels for up to 10 kHz bandwidth, 10-bit resolution biomedical signal transmissions. Different from other systems, the proposed wireless sensor employs a novel power management method for physiological signals to reduce power consumption. The proposed wireless sensor successfully transmits electrocardiogram (ECG) signals and four-channel electroencephalogram (EEG) signals with power consumptions of 92.7 and 56.8 mW respectively. It consumes 46% less power than the original sensor without power management (173 mW) in ECG acquisition and 67% less power in EEG acquisition. The circuit printed-circuit-band area in the proposed wireless sensor is 3.5×4.5 cm, suitable for various portable biomedical applications.