Passive damping using a piezoelectric device is a well-known technique. Both resistor and inductor loads connected to the piezoceramic are commonly used to attenuate a given resonance mode on a structure equipped with piezo dampers. The main drawback of this technique is its narrow band behavior and especially in the case of an inductor tuned passive piezo damper. The proposed technique is inherently wide band and does not rely on any tuned electric load. The piezoelectric device is simply continuously switched from open-circuit to short-circuit synchronously to the mechanical strain. It is called semi-passive because of the need of a sensor giving the strain of the piezo device. There is no need for external power supply unless for the low-level circuitry of the switch device. The damping efficiency appears to be twice what is obtained with pure resistive damping and is equivalent to what is achievable with a tuned inductor damper. It can work at any frequency without the need for large inductor especially for low frequency applications. A qualitative model gives an understanding of the damping mechanism.