This paper presents the design and fabrication of a single-layer out-of-plane thermal actuator. The step-bridge structure design enables bending and then buckling of the actuator in the out-of-plane direction by Joule heating. Moreover, the moving direction of the actuator can be specified by the step structure. In summary, the step-bridge actuator design has the following five merits: (1) The load-deflection relation is easily tuned; (2) the bistable buckling behavior is prevented; (3) the unwanted vibration modes can be suppressed; (4) the delamination problem is prevented; and (5) the bridge structure is stiffer and more stable. The actuator and its application on a lens positioning stage have been implemented using p++ Si layer by bulk micromachining. It demonstrates that a typical actuator would move upward with an amplitude near 13 mum when driven at 54 mW.