Investigation of electrical characteristics of fully- depleted SOI MOSFET and partially depleted SOI MOSFET devices in order to compare their electrical characteristics using Silvaco software was done and presented in this paper. The comparisons were focused on four main electrical characteristics that are threshold voltage, subthreshold voltage, leakage current and kink effect. The device structures and the characteristics were constructed, examined and simulated using Silvaco-Atlas. Results were analyzed and presented to show that the electrical characteristics of fully-depleted SOI devices are better than that of partially-depleted SOI devices.