A systematic investigation of the effects of high temperature (27° C to 300° C) on long N and P channel MOS transistors suitable for Large Scale Integration (LSI) is presented. The theory of the MOSFET is used to study the temperature behavior of the device's electrical parameters. The main temperature dependent parameters are the threshold voltage, the channel mobility, and the junction leakage currents. Zero-Temperature-Coefficient (ZTC) gate bias voltages are predicted, in the nonsaturation (linear) region, and in the saturation region of operation, for a given device. Criteria for the existence of such bias points are developed, and nonidealities of these points discussed. The large and small signal parameters of the MOSFET biased at its ZTC points are obtained. Detailed comparisons with experimental results will be reported in an accompanying paper .