An original micro-valve has been designed, modeled, fabricated and characterized. Its novelty resides in the thermal modification of the rigidity of its movable element by the phase transition of a fusible alloy integrated by self-assembly onto a silicon membrane. It is applied as a purge and safety valve for hydrogen micro fuel cells. The experimental results demonstrate the modification of the rigidity of the mechanical structure by melting and freezing one of its constituents, a property favored at a small size. This principle allows one to latch a mechanical element in the open and closed positions, as well as for ambient temperature sensing. Its potential applications include other devices such as electrical relays and optical switches, and can be integrated with active materials.