Method of fabricating tunneling transistor

A method of forming a tunneling transistor, comprising:

• forming a fin shaped structure in a substrate;
• forming a gate structure across the fin shaped structure;
• forming a first recess on one side of the gate structure formed across the fin shaped structure, and forming a second recess on an another side of the gate structure formed across the fin shaped structure, wherein the first recess comprises a sidewall having a first edge inclined toward the gate structure, and the second recess comprises a sidewall having a first edge inclined toward the gate structure;
• forming a source structure in the first recess;
• and
• forming a drain structure in the second recess, an entirety of the source structure and an entirety of the drain structure being of complementary conductivity types with respect to one another and having different materials, wherein the source structure comprises SiGe with a concentration of Ge therein being gradually decreased along a direction away from a channel region, and the drain structure comprises SiP with a concentration of C therein being gradually decreased along another direction away from the channel region.