A study of the substrate current was presented for a PD-SOI MOSFET under forward substrate bias. The substrate current is almost independent of the gate voltage and is dominated by the SSJ diffusion current for a bias above ~0.6V. BSIMSOI agrees only qualitatively with SENTAURUS simulations, and the model for the SSJ diffusion current must be reviewed in order to quantify accurately the substrate current and determine the impact in the power consumption of digital integrated circuits implemented with DTMOS.