Direct-current plasma immersion ion implantation (dc-PIII) is an emerging method for the treatment of planar samples and particularly attractive as an efficient and economical technique to fabricate silicon-on-insulator. In this article, we report the use of grid biasing to enhance the implantation efficiency such as implantation current density. Experiments in argon plasma show that the implantation current density varies with the biased voltage (V-g), is higher at V-g greater than or equal to + 30 V or V-g less than or equal to -40 V than at V-g = 0, and is saturated at V-g greater than or equal to +50 V or V-g less than or equal to -50 V at a pressure of 0.2 mTorr. The implantation current density is always higher at V-g = +50 V than at V-g = 0 at different pressure and radio-frequency (rf) power. Moreover, the implantation current density increases with the rf power and pressure at both 0 and +50 V biasing. The results of our particle-in-cell simulation and global model-show that the observed phenomenon is partly due to the variation of the plasma density with the bias, and the variation in the shape of emitted plasma surface with the bias is clearly illustrated by our experimental results. Similar results are observed for hydrogen plasma.