The I-V characteristics of the Permeable Base Transistor (PBT) has bee
n investigated in order to find a simple and practical model for use i
n circuit designs. Two possible approaches has been discussed, a one-d
imensional analytical solution and a semi-analytical solution mixing a
nalytical and empirical methods. The semi-analytical model developed i
n this paper offers high accuracy and a simple and fast evaluation. Al
l model parameters can be extracted from a set of I-V curves from two
typical transistors with different threshold voltages. An analytical s
mall signal model has been developed that agrees very well with two-di
mensional simulations.