High chemical etching resistance is strongly required for silicon nitride at low temperature such as 400°C or below in order to apply to the gate spacer, the contact etching stop layer, because various new materials which are thermally instable are introduced in order to improve the performance of MISFETs. High HF resistance of silicon nitride at the sidewall has been achieved by the plasma enhanced chemical vapor deposition using microwave excited high density plasma at 400°C. In this work, the electrical properties of those silicon nitride formed with various conditions were investigated for the gate spacer. The trap density that are attributed to the Si dangling bonds decreases as the SiH 4 flow rate decreases in this process. The leakage current can be suppressed by decreasing the SiH 4 flow rate below 3.0 sccm, because the stoichiometric silicon nitride can be formed in this range of process condition.