1/f noise has been investigated oil the drain to source voltage of deep sub-micron p-channel MOSFETs, with 5 mum channel width and 0.33-1.2 mum varying lengths. The MOSFETs were fabricated using 0.18 mum medium doped drain technology. The measurements were performed in strong inversion and linear operation region at room temperature. Noise parameters for BSIM3 simulation were extracted from the 1/f noise measurements. The oxide trap densities calculated from these noise parameters, however, showed a significant difference from transistor to transistor on the same die. Moreover, the drain voltage power spectral density exhibited a stronger dependence on channel length than the 1/L dependence expected from BSIM3 model. A modified BSIM3 model has been developed, based on threshold voltage variation along the channel. The modified model provides a good quantitative agreement with the noise power spectral density as a function of gate voltage. In addition, the modified flicker noise model more accurately predicts the oxide trap density. Carrier scattering coefficient was also obtained fi om the noise fitting parameters.