A thermal actuator for micro mechanical or micro electro-mechanical devices comprises a supporting substrate; an actuator extension portion; an anchor block extending from the substrate; a first group of at least two elongate corrugated arms attached at a first end thereof to a heating circuit at the anchor block and at a second end to the extension portion, the first group being arranged to be conductively heated through connection to the heating circuit; and a second group of at least two elongate corrugated arms attached at a first end to the anchor block and at a second end to the extension portion, the second group not being connected to a heating circuit and being spaced apart from the first group. The first edge of the at least two elongate corrugated arms of the first group and a first edge of the at least two elongate corrugated arms of the second group are in a common plane.