Abstract : Dynamic effects of avalanche-generated carriers in transistors were investigated using a two-dimensional, time-domain computer program. Basic properties of MESFET logic devices were also studied. The primary effect of avalanche process on bipolar transistor was found to be the majority carrier current in the lateral direction of the base creating a voltage drop opposite to the more usual edge-crowding effect. Avalanche multiplication in the stationary high field domain of a GaAs FET reduces device efficiency, but is usually not a destructive mechanism. Spontaneous avalanche in the gate-drain depletion region of the GaAs FET can spread to the drain and substrate leading to device failure. The intrinsic switching frequency of a logic device could approach, but not exceed, fT. In an IC, the switching speed depends mainly on gm of the device and capacitive loading of the circuit. Nonuniformity in the device and circuit parameters up to 10% would not significantly affect IC performance. (Author)