Improved large-signal models for the bipolar transistor are derived which are suitable for dc and transient computer-aided circuit analysis. The models are developed from the results of a two-dimensional analysis which yields the normal-active dc characteristics of the intrinsic portion of the transistor. Each of the models is formulated in terms of a measurable set of parameters which can theoretically be related to the low-level electrical parameters of the transistor and hence to its basic geometrical and physical characteristics. Based upon the dc model, two transient models are derived which correspond to one- and two-section approximations to the distributed nature of the intrinsic base as seen from the emitter-base terminals. The primary attribute of the single-section model, which corresponds in its complexity to commonly employed models, is its simplicity.