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The characteristics of an IGFET operating in saturation are developed in terms of an approximate two-dimensional model of the drain section of the space charge region. This section is treated as a volume obeying Gauss's law, thereby enabling the charge contained in it to be related to the integral of the electric displacement density normal to its surface without having to consider the detailed distribution of charge inside. An explicit expression is obtained for the drain conductance showing its dependence on device geometry, processing parameters and applied voltages. Closed form solutions for the current and conductance are obtained by neglecting the mobile carriers in the drain section. Substrate currents are evaluated using a simple impact ionization model.