The effect of high nitrogen concentration incorporation using decoupled plasma nitridation (DPN) of ultra-thin gate oxide (approximate to 15-17 Angstrom) on p-channel MOSFET performance has been investigated and compared with the conventional thermal nitridation process. Boron penetration is successfully suppressed in the ultra-thin gate dielectric prepared by the DPN process. This is confirmed by the measurements of gate leakage current, flat-band voltage shift and interface trap densities. The success in blocking boron penetration by DPN is attributed to its capability in incorporating a high level of nitrogen to near the top interface of the gate oxide. However, as a result of high level nitridation by DPN, a degradation in transconductance (Gm) is observed and interface trap density is also increased, compared to the conventional thermal nitridation process.