By using the surface piezoresistor diffusion method and front-side-releasing micromachining technique, we successfully developed a planar piezoresistive vibration sensor with less process cost, simple structure and less package difficulties. The functional features of the fabricated planar vibration sensors, including the amplitude–frequency response and random vibration response, have been evaluated comprehensively. As the results shown, the vibration sensor has reasonably good sensitivity performance (Min. detectable acceleration: 0.01g at the Min. responsible frequency of 4Hz; stable output at the measured signal with frequency >6Hz and amplitude >0.05g) for many applications: e.g. as the motion sensor for checking the health condition of human beings, or as the monitor sensor for monitoring the safety and security of infrastructure.