A method for manufacturing a
transistor and a
semiconductor device is provided. The method for manufacturing a
transistor may comprise: defining an active area on a
semiconductor substrate, and forming on the active area a
gate stack or a dummy
gate stack, a source / drain extension region, a spacer and a source / drain region, wherein the source / drain extension region is embedded in the active area and self-aligned on both sides of the
gate stack or dummy gate stack, the spacer surrounds the gate stack or dummy gate stack, and the source / drain region is embedded in the active area and self-aligned outside the spacer; removing at least a portion of the spacer to
expose a portion of the active area; and forming an interlayer
dielectric layer which covers the gate stack or dummy gate stack, the spacer and the exposed active area, wherein the
dielectric constant of the material of the interlayer
dielectric layer is smaller than that of the removed material of the spacer. It is beneficial for reducing the
capacitance between the gate region and the source / drain region as well as between the gate region and the contact plug.