first and second active regions 110 and 105 along the step thereof the gate electrode 113 is formed to be stacked on the gate insulating layer 111 the metal contact 123 is formed on the gate electrode 113 and the metal contact 125 is formed on the top of the junction region 115 on the other side of where the second active region 105 is formed on at this time the gate insulating layer 111 may be formed by diffusion of an oxidizing agent of the first and second active regions 110 and 105 and interface reaction with a silicon si material of the first and second active regions 110 and 105 referring to fig2 the diffusion of the oxidizing agent through a silicon oxide sio 2 previously formed is relatively more difficult in the stepped portion a of the gate insulating layer 111 that is the oxidizing speed is reduced at a bottom corner a of the second active region 105 as compared to a top and side of the second active region 105 therefore the gate insulating layer has a lower thickness at the bottom corner a when the silicon oxide sio 2 is formed through oxidation of silicon si of the second active region 105 stress is induced due to volume expansion the stress is concentrated on the bottom corner a and the oxidizing speed is reduced at that location therefore the gate insulating layer has a lower thickness at the bottom corner a in an embodiment the bottom corner a defines a sharp point where the gate insulating layer 111 is to be ruptured in an embodiment the second active region 105 having a rectangular shape is grown on the first active region 110.