Details are given of the design and operational features of two versions of a new multielectrode transistor which serves as a full adder for binary numbers in computer circuits. This transistor in a simple circuit connection performs the logical operations "and," "or," "exclusive or," "if-and-only-if," "neither-nor," "not both," and "not." The point-contact design utilizes two collectors with high current multiplication factors to provide signal amplification during the logical operation at very high speeds. The "all-junction" design utilizes p-n hook collectors to give much higher values of intrinsic alpha. The paper describes the nature of the internal positive-feedback action in the two-collector transistors and illustrates the function of these transistors as logic devices.