A method for fabricating a semiconductor structure is shown. A first gate of a first device and a second gate of a second device are formed over a semiconductor substrate. First LDD regions are formed in the substrate beside the first gate using the first gate as a mask. A conformal layer is formed covering the first gate, the second gate and the substrate, wherein the conformal layer has sidewall portions on sidewalls of the second gate. Second LDD regions are formed in the substrate beside the second gate using the second gate and the sidewall portions of the conformal layer as a mask.