Method for fabricating semiconductor device

A method for fabricating semiconductor device, comprising:

• forming a gate dielectric layer on a substrate;
• forming a gate material layer on the gate dielectric layer;
• removing part of the gate material layer and part of the gate dielectric layer to form a gate electrode, wherein a top surface of the gate dielectric layer adjacent to two sides of the gate electrode is lower than a top surface of the gate dielectric layer between the gate electrode and the substrate;
• forming a first mask layer on and directly contacting the gate dielectric layer and the gate electrode;
• removing part of the first mask layer and part of the gate dielectric layer in one etching step to form a first spacer and divide the gate dielectric layer into a top portion and a bottom portion, wherein the first spacer directly contacts sidewalls of the gate electrode and a thickness of the top portion is equal to a thickness of the bottom portion;
• forming a second mask layer on the substrate and the gate electrode after forming the first spacer;
• and
• removing part of the second mask layer to form a second spacer, wherein a large portion of the first spacer and the second spacer are substantially parallel and vertically arranged, and the first spacer and the second spacer converge at a junction point between a top surface and a sidewall of the gate electrode.