This paper describes a unified framework to model the floating-body effects of various SOI MOSFET operation modes, including body-contacted mode, partially depleted mode and fully depleted mode. As the operation mode is dimension and bias dependent, different modes can co-exist in a single SOI technology. A smooth transit from one type of operation mode to another is thus essential and has been included in the model. In addition, the floating-body effects can couple to a number of other SOI specific phenomena such as heating assisted impact ionization, gate tunneling induced dynamic behavior, and operation mode dependent small signal output resistance. A methodology to model the overall SOI MOSFET behavior due to the combination of multiple floating-body related effects will also be described.