This paper proposes a new approach towards mechanical waste energy scavenging, using a micromachined electrostatic converter. The device consists of a vibration sensitive variable capacitor polarized by an electret. The variation of the capacitance results in a current through a load circuit. A physical model of the device is described; in order to obtain a closed form expression for the converted power a linear model is presented. This model shows that 50 muW can be generated with a 5 gm vibration. A first prototype design based on a SOI MPW-service is proposed.